
Class __l5i4ai 

Book Esr 



SMITHSONIAN DEPOSIT 



HUME: 

THE RELATION OF ^ / V^ 

THE TREATISE OF HUMAN NATURE— BOOK I / ^TU 
TO THE INQUIRY CONCERNING 
HUMAN UNDERSTANDING 

THESIS 

PRESENTED TO THE 

University Faculty of Cornell University 

FOR the 

Degree op Doctor of Philosophy 



BY 

WILLIAM BAIRD ELKIN 



4-1 0/ j "-} 



ITHACA, N. Y. 
1904 










Press of 
The New Era PRmriHG Company, 

kAHCASIER, PAi 



PREFACE. 



This thesis contains the first seven chapters of a 
more extended work which is now being published 
by the Macmillan Company of New York. In addi- 
tion to what is here presented the complete work 
treats, in separate chapters of the following topics : 
Belief; Probability, Necessity, and the Reason of 
Animals; Material Substance and External Exist- 
ence; Spiritual Substance, Self, and Personal Iden- 
tity; Miracles, a Particular Providence, and a Future 
Life; Conclusion. There are also two Appendices, 
the first of which consists of an Outline of the Rela- 
tion of the Treatise to the Inquiry, while the second 
is a Bibliography of the literature on Hume. 

W. B. E. 

Columbia, Mo. 
May 31, 1904. 



CONTENTS. 

CHAPTEE I. 

Introduction. 

Page. 

§ 1. Preliminary Remarks 1 

§ 2. Aim 4 

§ 3. The General Relation of the Treatise and In- 
quiry to Hume's other Philosophical Works. . 6 
§ 4. The General Relation of the Treatise and In- 
quiry to each other 10 

I. With regard to Form 10 

II. With regard to Content 16 

§ 5. Mode of Procedure 23 



CHAPTER II. 

Hume's Aim, Subject-Matter, and Method. 

§ 6. Hume's Aim 24 

§ 7. Hume's Subject-Matter 41 

§ 8. Hume's Method- 45 

CHAPTER III. 

Perceptions: their Nature, and Cause. 

§ 9, The Nature, and Classification of Perceptions. . 50 

§10. The Cause of Perceptions 59 

I. Epistemological 60 

II. Physiological 63 

§11. Conclusion 69 

T 



vi Hume's treatise and inquiry. 

CHAPTEE IV. 

Association of Ideas, and Eesult — Complex Ideas. 

Page. 

§12. Association of Ideas " 71 

§13. Complex Ideas 77 

I. Philosophical Kelations 77 

II. General or Abstract Ideas 83 

§14. Conclusion 86 



CHAPTEE V. 

Space and Time. 

§15. The Idea of Infinite Divisibility 89 

§16. The Idea of Space 91 

§17. The Idea of Time 95 

§18. The Treatment of Space and Time in the Inquiry 95 

§19. Conclusion 98 

CHAPTEE VI. 

Theory of Knowledge. 

§20. The Faculties of Mind 102 

§21. Intuitive Knowledge 106 

§22. Demonstrative Knowledge — Mathematics Ill 

I. The Epistemological Exposition 113 

II. The Logical Exposition 117 

III. The Psychological Exposition 123 

IV. Conclusion 124 

§23. The Treatment of Mathematics in the Appendix 125 
§24. The Treatment of Mathematics in the Inquiry. . 126 
§25. The Treatment of Mathematics in Hume's other 

Philosophical Writings 132 

§26. Conclusion 134 



CONTENTS. VU 

CHAPTER VII. 

The Idea of Cause and Effect. 

Page. 
§27. Causation the basis of all Reasoning Concern- 
ing Matters of Fact 140 

§28. Examination of the Idea of Cause and Effect. . . 142 

I. The General Question of Causation 144 

II. The Particular Question of Causation 146 

III. The Idea of Necessary Connection 151 

IV. Conclusion 155 

§29. Some Misconceptions of Hume's Critics 157 

§30. Conclusion 168 



CHAPTER I. 



INTRODUCTION. 



§ 1. Preliminary Remarks.— The history of Eng- 
lish empirical philosophy is sometimes likened to a 
drama in five acts. In the first act, a system of em- 
piricism is inaugurated by Bacon; in the second and 
third, the dialectic movement is gradually unfolded by 
Hobbes and Locke; in the fourth, the usual compli- 
cations arise through the criticisms and transforma- 
tions of Berkeley ; finally, in the fifth, the scene closes 
with the annihilating catastrophe of Hume.^ 

But as Hume marked the melancholy close of the 
era of sensationalism, he heralded the inspiring dawn 
of a brighter epoch, the era of idealism, and at the 
same time laid the foundation for a synthesis of the 
two, in the more scientific movement of the present 
age. Reid in Scotland and Kant in Germany were 
awakened, almost simultaneously, from their dogmatic 
slumbers, by the subtle and irresistible dialectic of the 
great skeptic. British and German philosophy, how- 
ever, when drifting peacefully toward a euthanasia, 
far from being overwhelmed by the storm of Hume's 
criticism, were only instigated thereby to make a new 
tack in the never-ending pursuit of speculative truth. 
With felicity no less than impressiveness, Sir William 
Hamilton, in his introductory lecture in 1836, de- 
clared : ' ' The man who gave the whole philosophy of 

* Cf. Grimm, Ztir GescMchte des Erkenntnisprohlems von 
Bacon zu Hume, Vorwort. 

1 1 



2 Hume's teeatise and inquiry. 

Europe a new impulse and direction, and to whom, 
mediately or immediately, must be referred every sub- 
sequent advance in philosophical speculation, was our 
countryman— David Hume. . . . The skepticism of 
Hume, like an electric spark, sent life through the 
paralyzed opinions; philosophy awoke to renovated 
vigor, and its problems were again to be considered 
in other aspects, and subjected to a more searching 
analysis. ' ' 

It matters little in what manner the position of 
"the last great English philosopher" be designated 
in the history of speculative thought, for his system 
is so unique, and so significant that it will always 
awaken the most profound reflection, as well as merit 
the most candid examination. The study of Hume's 
works, however, is unusually perplexing, and the true 
significance of his philosophy of human nature ex- 
tremely difficult accurately to determine, partly, be- 
cause of the different phases of thought, obscurities, 
ambiguities, and even inconsistencies that appear in 
his writings, but chiefly, because of the twofold ex- 
position of his system. Before a just estimation of 
his philosophy can be arrived at, the more important 
relations subsisting between his philosophical writings 
must be ascertained. It is, therefore, a question of 
much interest what the relations of his chief works 
are to one another. Moreover, this question is also 
one of much importance. For although Hume's in- 
fluence is not perhaps so great now as when James 
Hutchison Stirling wrote -} ' ' Hume is our Politics, 
Hume is our Trade, Hume is our Philosophy, Hume is 
our Religion,— it wants little but that Hume were even 

The Secret of Eegel, p. Ixxiii. 



INTRODUCTION. 6 

our Taste," his once striking position in philosophical 
and political thought is still justly prominent. ''The 
Treatise of Human Nature and the Critic of Pure 
Reason," remarked his most relentless critic,^ "taken 
together, form the real bridge between the old world" 
of philosophy and the new. They are the essential 
'Propaedeutic,' without which no one is a qualified 
student of modern philosophy." 

Hume's great philosophical work is A Treatise of 
Human Nature. It consists of three books: I, "Of 
the Understanding"; II, "Of the Passions"; III, 
"Of MovsiW ;—i7itellect, feeling, and will. The first 
two volumes were published in 1739, and the third 
in 1740. It seems, however, that the book was writ- 
ten as early as 1736, when Hume was only twenty- 
five years old.^ True, in accordance with one of the 
author's distinctive characteristics, it was contin- 
ually revised, up to the very time of publication.^ Yet 
the changes which were made appear to have dealt 
with form more than with content ; and so far as they 
had reference to content, they were made rather in 
the way of omission, than in the way of development.* 
But the Treatise of Human Nature awakened no in- 
terest, and received almost no notice; it "fell dead- 
horn from the press,"— to use the expressive words 
of the author. Nevertheless, Hume, thinking that he 

1 Hume's Philosophical Works, I. Green's " Introduction," p. 
3. — The references throughout are to the Green and Grose edi- 
tion; I, 1890; II, 1882; III and IV, 1889. Since I, contains 
the Treatise and IV, the Inquiry, in explicit references to these 
works the volume number is not given. 

^ Cf. Burton, Life and Correspondence of David Hume, I, 
pp. 98, 337. 

'Ibid., I, pp. 62, 63. 

* Ibid., pp. 63, 64. 



4 Hume's treatise and inquiry. 

had made a mistake in piiblisliirLg too early, still be- 
lieved that his system of philosophy was of permanent 
value.' Hence, he revised the Treatise of Human 
Nature, and published it in much briefer, and more 
popular form. The abbreviated work appeared as 
follows : Philosophical Essays concerning Human Un- 
derstanding, 1748; An Inquiry concerning the Prin- 
ciples of Morals, 1751 ; A Dissertation on the Passions, 
1757. It is only with the first book of each group 
that I propose to deal in the present volume. These 
books will be designated respectively, for the sake of 
convenience and in accordance with common usage, 
the Treatise, and the Inquiry. Reference, of course, 
will be made, from time to time, to Hume's other 
philosophical writings, for the purpose of throwing 
additional light upon the subject, or in order to obtain 
a more comprehensive view of the matter under dis- 
cussion. 

§ 2. Aim. — There is a general impression that the 
position which Hume adopted in the Inquiry is not 
identical with that which he had previously as- 
sumed in the Treatise, and consequently, that the 
philosophical principles of the later work are not 
exactly the same as those of the earlier. It is 
sometimes said that the Inquiry represents the posi- 
tion of the empiricist, or positivist, while the Treatise 
represents the position of the skeptic;— as was re- 
marked recently by one of the most brilliant philo- 
sophical writers of our time:* "The Treatise is the 
close of sensationalist philosophy, the Inquiry the be- 
ginning of common sense philosophy." Hence, it is 

1 Hume, My Oivn Life. 

^Sehurman, The Philosophical Revieio, Vol. VII, p. 10, n. 



INTRODUCTION, 5 

inferred that the later work, not being so negative as 
the earlier, represents an important change as having 
occurred in the author's thought when his mind be- 
came more mature/ On the other hand, some writers 
assert that the position, or standpoint of both books 
is essentially the same. ' But then, regarding the ex- 
act nature of that position there are again differences 
of opinion; Huxley,* for example, insisting that it 
is mainly positive, and Green* maintaining that it is 
chiefly negative. If we appeal to the testimony of 
the author himself, this confusion is by no means re- 
moved. For in the advertisement to the second vol- 
ume of the posthumous and authoritative edition of 
his Essays and Treatises on Several Subjects— a vol- 
ume containing the Inquiry,— not only does Hume 
complain that "several writers, who have honored 
the author 's philosophy with answers, have taken care 
to direct all their batteries against the juvenile work, 
which the author never acknowledged," but he con- 
cludes as follows:* "Henceforth, the author desires, 
that the following pieces may alone be regarded as 
containing his philosophical sentiments and prin- 
ciples." Yet on another occasion, in a letter to Gil- 

1 Cf. Burton, Life, I, pp. 120, 273, 274; Erdmann, History of 
Philosophy, II, p. 128; Falckenberg, Gesch. d. neueren Phil., 
second ed., p. 185, n. 2; Hyslop, Hume's Treatise on Morals, 
p. 17; Hunt, Contemporary Review, Vol. XI, p. 77. 

2 Cf. Green, " Introduction to Hume " ; Huxley, Hume, pp. 
11, 45; Webb, Veil of Isis, p. 71; McCosh, Hist, of Scottish 
Phil., p. 123; Jahn, D. H. Causalitdtstheorie, p. 6. 

^ Hume, pp. 51, 60. 

* Hume's Philosophical Works, Preface to Vol, I, and General 
Introd. 
6 Ibid., Ill, p. 38. 



6 Hume's teeatise and inquiry. 

bert Elliot, he says:^ "I believe the Philosophical 
Essays [the Inquiry] contain every thing of eon- 
sequence relating to the understanding, which you 
would meet with in the Treatise ; and I give you my 
advice against reading the latter. By shortening 
and simplifying the questions, I really render them 
much more complete. Addo dum minuo. The philo- 
sophical principles are the same in both; but I was 
carried away by the heat of youth and invention to 
publish too precipitately." To clear up this ob- 
scurity on the question regarding Hume's exact posi- 
tion in his two chief philosophical works is the aim 
of the present investigation. 

§ 3. The General Relation of the Treatise and In- 
quiry to Hume's other Philosophical Writings.— "Be- 
fore entering upon the work in detail, it may be well 
to indicate, in a general way, the relation in which 
these two books stand, (1) to the philosophical writ- 
ings with which they are connected, and (2) to each 
other. The first of these topics will be treated in 
the present section, the second, in the following sec- 
tion. 

As has already been said, it is only the first book 
of each group that falls within the scope of this 
investigation. But here two questions at once sug- 
gest themselves: (1) "What are the relations of the 
different books within each group to one another? 
and (2) Can the relation of the Treatise to the In- 
quiry be thoroughly examined without taking account 
also of the books with which these two are respectively 
connected ? Leaving aside the second question for the 
moment, we find a partial answer to the first, in the ad- 

1 Burton, Life, I, p. 337 ; cf . p. 98. 



INTRODUCTION. 7 

vertisement to Books I and II of the Treatise of Hu- 
man Nature. "The reader must only observe," says 
Hume, "that all the subjects I have there planned 
out to myself, are not treated of in these two volumes. 
The subjects of the Understanding and Passions make 
a complete chain of reasoning by themselves; and I 
was willing to take advantage of this natural division, 
in order to try the taste of the public. If I have the 
good fortune to met with success, I shall proceed to 
the examination of Morals, Politics, and Criticism; 
which will complete this Treatise of Human Nature. ' ' 
Here it is seen that Hume regarded Books I and II 
as forming a connected piece, thus practically con- 
stituting one book. But the relation of these two 
volumes to the third is not so close, as the author has 
already indicated, and as he afterwards specifies 
more definitely in the advertisement to Book III. ''I 
think it proper to inform the public," he says, "that 
though this be a third volume of the Treatise of 
Human Nature, yet it is in some measure independ- 
ent of the other two, and requires not that the reader 
should enter into all the abstract reasonings con- 
tained in them. ... It must only be observed, that 
I continue to make use of the terms, impressions and 
ideas, in the same sense as formerly." From these 
quotations we learn that Hume's philosophy, so far 
as it is presented in the Treatise of Human Nature, 
falls into two general divisions which are, in large 
measure, independent of each other, viz., the phi- 
losophy of the understanding and passions on the one 
hand, and the philosophy of morals on the other. 

In the first section of the Inquiry, the author 
adopts the twofold classification of mental science 



8 Hume's treatise and inquiry. 

which the Latins had inherited from the Greeks, 
which the scholastics had popularized, and which pre- 
vailed in occidental philosophy generally, until super- 
seded by the tripartite division of Kant;— a division 
which, through the present dominating influence of 
the biological sciences, is again giving place to the 
Aristotelian classification. Hume states that moral 
philosophy or the science of human nature "may be 
treated after two different manners," abstractly, or 
concretely.^ And besides making this distinction in 
method, he recognizes a corresponding division of sub- 
ject-matter, viz., the "abstruse" or theoretical phi- 
losophy, and the "easy" or practical; the former be- 
ing conversant with the understanding, and the latter 
with the feelings and will. Thus he asserts :^ ' ' There 
are many obvious distinctions [between the powers 
and faculties of the mind] , such as those between the 
will and understanding, the imagination and passions, 
which fall within the comprehension of every human 
creature." This same division is implied in the first 
book of the Treatise of Human Nature,^ and is ex- 
plicitly made in the third book,* Consequently, 
Hume's philosophy, so far as it is presented in the 
Treatise of Human Nature, and in the Inquiries and 
Dissertation— tlcms omitting Polities and Criticism, 
subjects with which we have no direct concern, — 
although falling externally into three divisions, may 
properly be regarded as consisting of two parts, 
theoretical, and practical. Theoretical philosophy is 
treated in Book I of the Treatise of Human Nature, 

"■ Pp. 3, 4. 
*P. 10. 
» I, p. 543. 
* II, pp. 235, 236. 



INTRODUCTION. y 

and in the hiquiry concerning Human Understanding. 
While practical philosophy is treated in Books II and 
III of the Treatise of Human Nature, and in the Dis- 
sertation on the Passions and the Inquiry concerning 
the Principles of Morals. 

We come now to a closer examination of our ques-" 
tion. What are the relations of dependence in which 
the books within each group stand to one another? 
An answer is found in the second section of Book I, 
and in the first section of Book II of the Treatise of 
Human Nature. All the perceptions of the mind are 
impressions and ideas. All impressions and ideas 
are those of sensation, and those of reflection. It 
may be said that Book I treats of impressions and 
ideas of sensation/ Books II and III of impressions 
and ideas of reflection. Now, since impressions of 
sensation are the perceptions that appear first in the 
mind, while ideas of sensation are but copies of these ; 
and since impressions of reflections arise ' ' either from 
the original impressions, or from their ideas ;"2 the 
treatment of impressions and ideas of reflection will 
be dependent on that of impresions and ideas of sen- 
sation, and not vice versa. Consequently, Books II 
and III are dependent on Book I, but Book I is not 
dependent on Books II and III. In the Inquiries 
and Dissertation the two sections just mentioned are 
omitted. Moreover, among these works there is no 
connection indicated, except the general relation be- 
tween the subjects of which they treat, theoretical 
philosophy, and practical. The Inquiries and Dis- 
sertation were not only written at different times, but 

' Cf. I, p. 380. 
*II, p. 76. 



10 Hume's teeatise and inquiry. 

also in a chronological order different from that of 
the corresponding books of the Treatise of Human 
Nature. They stand, therefore, practically, in no 
relation of dependence upon one another. 

It is now easy to answer the second question, viz.. 
Can the relation of the Treatise to the Inquiry prop- 
erly be investigated without a special examination of 
Hume's other philosophical writings? The answer 
is in the affirmative, for the following reasons:— (1) 
Only the first two books of the Treatise of Human 
Nature are closely connected, and regarding them, 
there is a relation of dependence only on the part of 
the second. .{2) The Inquiries and Dissertation are, 
practically, not only separate works, but also inde- 
pendent. (3) The Treatise and Inquiry contain all 
of Hume's epistemology and metaphysics that is of 
permanent or real value for the history of philosophy. 

§ 4, The General Relations of the Treatise and 
Inquiry to each other.— We turn now for a moment 
to the general relations in which the Treatise and 
Inquiry stand to each other. These may be consid- 
ered under the two heads of form, and content. 

I. The General Relation of the Treatise to the In- 
quiry with regard to Form. Here two points may 
be noted, style, and arrangement. 

1. Style. Dr. Johnson said that Hume's style was 
not English but French. Johnson, however, was not 
an unbiased critic of Hume. Yet Grose admits that, 
so far as the structure of sentences is concerned, 
Hume was influenced by the literature of France at 
the time he wrote the Treatise.^ We think it may 
be questioned, whether the French element— if such 

"■ III, p. 40. 



INTRODUCTION. 11 

it can be called— in Hume's style was not due more 
to immatureness and originality, than to the influence 
of French literature. The numerous Scotticisms are 
significant of the author's provincialism, as well as of 
his immaturity. Notwithstanding the many expres-. 
sions of candor, diffidence, hesitation, and skepticism, 
there is not a little pedantry, superficiality, egotism, 
and dogmatism. ' ' This work, ' ' observed his reviewer, ^ 
"abounds throughout with egotisms. The author 
could scarcely use that form of speech more fre- 
quently, if he had written his own Memoirs." Now 
and then, there occurs an expression of insincerity, 
irony, or ambiguous humor, which is extremely puz- 
zling. In some of the repetitions, what is evidently 
meant to be the same thing is expressed so differently 
that it is no longer the same. And besides Hume's 
philosophical mode of expression, there is his habit 
of speaking with ''the vulgar." These two forms 
of statement occasionally mingle with each other, or 
at least seem to mingle, with the result that the 
reasoning, at times, becomes inextricably confused. 
Nevertheless, Knight^ speaks in high appreciation of 
the "admirable literary form" of the Treatise, and 
its unequalled lucidity, both of thought and of ex- 
pression." But with Knight's opinion, respecting 
the lucidity of the Treatise, very few students of 
Hume— and probably none except Scotsmen,— no 
matter how enthusiastic they may be in praise of 
"the master," will be able to concur. 

In the Inquiry, the Scotticisms and French phrase- 
ology have been superseded by the smooth and 

1 The Works of the Learned, Nov., 1739. 

2 Hume, p. 26; cf. Burton, Life, I, p. 91. 



12 Hume's teeatise and inquiry, 

polished diction, so characteristic of Hume's later 
writings. Redundancy, in most cases, has been trans- 
formed to brevity. The depth of thought and labored 
mode of expression of the philosopher have, in large 
measure, given place to the superficiality and elegance 
of the author. Hence, while the Treatise is a difficult 
book to read, the Inquiry is an easy one. Hume thus 
realized, in part at least, the wish that he expressed 
at the close of the first section: "Happy, if we can 
unite the boundaries of the different species of phi- 
losophy, by reconciling profound inquiry with clear- 
ness, and truth with novelty ! ' ' 

This change of style, in the later work, is easily ex- 
plained. In the introduction to the Treatise Hume 
remarked:^ ''No man needs ever despair of gaining 
proselytes to the most extravagant hypothesis, who 
has art enough to represent it in any favorable 
colors. " In a letter to Hutcheson, in 1740, he wrote :^ 
"I wish I could discover more fully the particulars 
wherein I have failed. I admire so much the candor 
I have observed in Mr. Locke, yourself, and a very 
few more, that I would be extremely ambitious of 
imitating it, by frankly confessing my errors." In 
the Autobiography he asserted: "I had always en- 
tertained a notion, that my want of success in pub- 
lishing the Treatise of Human Nature, had proceeded 
more from the manner than the matter, and that I 
had been guilty of a very usual indiscretion, in going 
to the press too early." And in the first section of 
the Inquiry' he aclmowledges that the abstractness of 
philosophical speculations "is no recommendation, but 

^P. 30G. 

-Burton, Life, 1, p. 117. 

3 III, p. 3. 



INTRODUCTION. 13 

rather a disadvantage to them," and that ''this diffi- 
culty may perhaps be surmounted by care and art, 
and the avoiding of all unnecessary detail." It is 
not surprising, therefore, that Hume toiled inces- 
santly, Avith unwearying pains, to acquire a good 
English style ;^ nor is it remarkable that his persistent 
efforts were crowned with the most gratifying suc- 
cess. In due time he became "the one master of 
philosophic English. ' ' * 

Still another cause that might be assigned for the 
change of style, in the Inquiry, was the author's de- 
sire to suit his work to the taste of his readers.^ For 
the third volume of the Treatise of Human Nature 
was written "in an age, wherein the greatest part 
of men [seemed] agreed to convert reading into an 
amusement, and to reject every thing that [required] 
any considerable degree of attention to be compre- 
hended."* And the Inquiry was prepared in a 
period which Hume implicitly characterized in a 
similar manner.* Whereas, the first volume of the 
Treatise of Human Nature was written at a time when 
"personal identity" had become "so great a ques- 
tion in philosophy," especially in England, "where 
all the abstruser sciences [were] studied with a pecu- 
liar ardor and application."^ 

2. Arrangement. Concerning arrangement, the 
writers on Hume, in accordance with their usual cus- 

1 Biu-tou, Life, II, pp. 79-81 ; cf. Tytler, Memoirs of the Life 
and Writings of Henry Home of Karnes, I, pp. 170-173. 

2 III, p. 40. 

3 Of. Burton, Life, I, pp. 62, 63, 273. 
« II, p. 234. 

5 Cf. IV, pp. 4-12. 

6 1, p. 539; cf. p. 308. 



14 hume's treatise and estquiey, 

torn, differ diametrically in opinion. Burton states : ^ 
' ' It has been generally and justly remarked, that the 
Treatise is among the least systematic of philosophical 
works— that it has neither a definite and comprehen- 
sive plan, nor a logical arrangement." On the other 
hand, Adamson declares:^ "The course of Hume's 
work follows immediately from his fundamental prin- 
ciple, and the several divisions of the Treatise, so far 
as the theoretical portions are concerned, are but its 
logical consequences." While the first view here ex- 
pressed is inaccurate, and the second is inadequate; 
yet in the former, there is an element of truth, as in 
the latter, there is an implication of error. The cor- 
rect view, as indeed one might expect, lies about mid- 
way between the two extremes.' The Treatise, as a 
whole, is systematically arranged, but detailed por- 
tions are not. If the work be viewed in its entirety 
methodical arrangement, according to a definite plan, 
is clearly manifest. Thus Part I gives an account of 
the contents of the individual mind, of impressions 
and ideas, or of what Hume calls "the elements" of 
the philosophy of human nature .* Part II treats of 
the ideas of space and time, and Part III deals with 
the idea of cause and effect; that is. Part II may be 

1 Life, 1, p. 66 ; cf. Ritchie, Life of Hume, p. 305 ; Meinong, 
Hume-Studien, II, p. 27; Knight, Hume, p. 28. 

2 Ency. Brit., ninth ed., art. Hume, p. 352 ; cf. Jacob, David 
Hume iiher die menschlicJie Natur, 1, p. 532; Brede, Der 
UnterscMed d. Lehren Humes im Treatise ti. ini Inquiry, p. 
2, n. 

3 Cf. Grimm, Zur Gesch. d. Erkenntmsprohlems, pp. 573- 
576; Jodl, Leben u. Phil. D. H., p. 200; Pfleiderer, Empirismus 
u. Skepsis in D. H. Phil., p. 132. — Grimm's treatment of this 
question is the best that has yet appeared. 

^I, p. 321. 



INTRODUCTION. 15 

said to treat of the abstract element of human knowl- 
edge, while Part III deals with the concrete element. 
Finally, Part IV explains the ideas of self and sub- 
stance, exhibiting the logical resvilts of the previous 
treatment, and expressing the relation of the knowing 
consciousness to known objects ; that is, it investigates 
the relation of knowledge to the supposed self and ex- 
ternal things, the relation of impressions and ideas as 
cognitive to impressions and ideas as cognized.^ 

There is also a gradual transition between the prin- 
cipal divisions of the work. The last section of Part 
I deals with general ideas, and prepares the way for 
the discussion of the ideas of space and time in Part 

II. The last section of Part II, treating of the ideas 
of existence and external existence, serves as an in- 
troduction to Part III.'' And the last section of Part 

III, ''Of the Reason of Animals," besides containing 
an argument in confirmation of the truth of Hume's 
system, as thus far presented, is at the same time a 
preparation for what follows in Part IV. When one 
descends to further particulars, however, one finds 
that the minor divisions of the book are often ill- 
arranged, both in their relations to one another, and 
in their internal structure. At one time the reason- 
ing is fragmentary; at another, it is long drawn out, 
stated in different ways, or repeated to weariness. 
Not only are the arguments disproportioned, but 
essential matter is sometimes mingled with non- 
essential; trivial paradoxes are occasionally intro- 
duced, or terms are used with varying meanings, until 
the central thought becomes almost completely ob- 

1 Cf. Adamson, Ency. Brit., art, Hume, p. 352. 
» I, p. 369. 



16 Hume's treatiISe and inquiry. 

scured by attendant circumstances, or inextricably 
confused through, perplexing ambiguities. 

Since the later work is, in some measure, a recast 
of the earlier, the general order of discussion is sim- 
ilar in both. But inasmuch as portions of the Treatise 
are omitted in the Inquiry, and new material is in- 
troduced, while the resulting treatment is clearer, 
freer from ambiguities and contradictions, the ar- 
rangement of the later work is less systematic than 
that of the earlier. The points of transition, formerly 
observable, do not appear in the Inquiry. Abstract 
ideas are treated here only in the last section, and 
then merely incidentally. The ideas of existence and 
external existence are scarcely mentioned. And the 
section on the reason of animals is entirely cut off 
from related topics by new material. These changes, 
except that arising from the introduction of new 
matter — a subject on which more will be said pres- 
ently,— may be accounted for by the abridged form 
of the later work. But then the question immediately 
arises, Why was the later work abbreviated? This 
inquiry brings us to the next subject for discussion, 
and will be dealt with in the remaining part of the 
present section. 

II. The General Relations of the Treatise to the 
Inquiry with regard to Subject-matter. The Inquiry 
is mainly a restatement, in abbreviated form, of cer- 
tain portions of the Treatise, Parts I and III. To 
Henry Home, in 1737, Hume wrote :^ ' ' I am sorry I 
am not able to satisfy your curiosity by giving you 
some general notion of the plan upon which I proceed. 
But my opinions are so new, and even some terms 

^ Burton, Life, I, p. 62. 



INTRODUCTION. 17 

that I am obliged to make use of, that I could not 
propose, by any abridgment, to give my system an air 
of likelihood, or so much as make it intelligible. It 
is a thing I have in vain attempted already, at a 
gentleman's request in this place, who thought it 
would help him to comprehend and judge of my 
notions, if he saw them all at once before him. ' ' The 
difficulty here referred to may be the cause why 
Hume, instead of giving a summary or outline of his 
philosophy, in the Inquiry, presents a full statement 
of some subjects, gives an abridgment of others, and 
omits others entirely. Thus Parts I and III are 
largely rewritten. But the only division correspond' 
ing to Parts II and IV is section xii. And this sec- 
tion, although it deals to some extent with nearly all 
the topics that are treated in the corresponding por- 
tions of the earlier work, is by no means an adequate 
abstract or synopsis of them. 

It is interesting to learn from a letter of Hume, in 
1755, to his publisher, Millar,^ that Part II of the 
Treatise was rewritten. The monograph, however, 
never appeared. As a reason for not publishing this 
revision, Grose^ suggests that "perhaps the author 
despaired of the subject being popular." Other 
writers on Hume have also expressed their opinions 
on this question. But in general, their views are 
mere conjectures, groundless as they are various. The 
only reason positively known, why this revision of 
Part II was not published, is that given by the author 
himself in a letter to Strahan : ' "I intended to print 

^ Burton, Life, I, p. 421. 

" III, p. 60. 

3 Hill, Letters of David Hume to William Strahan, p. 230. — 
For many years it was supposed that Hume's letters to 



18 Hume's treatise and inquiry. 

four Dissertations," he says, "the natural History of 
Religion, on the Passions, on Tragedy, and on the 
metaphysical Principles of Geometry. I sent them 
up to Mr. Millar; but before the last was printed, I 
happened to meet with Lord Stanhope, who was in 
this country, and he convinced me, that either there 
was some defect in the argument or in its per- 
spicuity; I forget which; and I wrote to Mr. Millar, 
that I would not print that Essay." Were one 
controversially inclined, one might now undertake 
to show that the former of the two reasons, here 
mentioned, was the chief one why the ''Metaphysical 
Principles of Geometry" was not printed. For de- 
fect in perspicuity, although a sufficient reason why 
the dissertation should not appear as a part of the 
Inquiry, is not a satisfactory explanation why, when 
in the form of an essay, it should have been sup- 
pressed for all time. It is not worth while, however, 
to carry the discussion of this point farther; for the 
fact, that the author forgot whether the defect was in 
the "argument" or in the "perspicuity," tends to 
imply that the essay was open to criticism in both 
these respects. 

Hume also gives a hint why some important por- 
tions of Part IV were omitted in the later work. In 
the appendix to the Treatise^ he confesses that, on a 
more strict review of the section concerning personal 
identity, he found himself involved in such a laby- 
rinth, that he knew neither "how to correct" his 
Strahan had been destroyed, as it was Strahan's custom not to 
preserve the letters which he received; cf. Burton, Life, II, 
p. 477, n. 2. 

^ I, pp. 558, 559 ; cf, Grinun, Zur Oesch. d. ErJcenntnisproi- 
lems, pp. 580, 582. 



INTRODUCTION. 19 

former opinions, nor "how to render them con- 
sistent." This acknowledgment indicates that, soon 
after the publication of the Treatise, Hume per- 
ceived perfectly well one of the main difficulties in- 
herent in his system. It is significant, therefore, that 
in the Inquiry, not merely is the question of personal 
identity omitted, but the other more important sub- 
jects, in the discussion of which inconsistencies or 
absurdities become most apparent, are also either 
omitted entirely, or are only incidentally referred 
to; for example, philosophical relations, space and 
time, mathematics, substance— material and spiritual 
— and an external world. Now all these subjects, 
except philosophical relations, are treated in Parts 
II and IV of the earlier work. The conclusion, 
therefore, is unavoidable, that Hume, when preparing 
the Inquiry for publication, being extremely anxious 
to have his theory of knowledge appear in a favorable 
light before the public, was swayed by the character- 
istic shrewdness of the "canny" Scotsman, and pur- 
posely omitted, or left in the background, these diffi- 
cult and perplexing questions. 

Some writers think that Hume omitted, in the In- 
quiry, his doctrine of substance lest it should prej- 
udice the work in the eyes of the public;^ and others 
assert that he omitted the doctrine of personal ident- 
ity, lest it should shock too severely religious senti- 
ment.^ The former of these views may contain an 
element of truth, but the latter is entirely erroneous. 
Hume was much more considerate toward the religious 
sentiments of the people when preparing the Treatise 

' Cf. Seliy-Bigge, Hume's Enquiries, Introd. 

*Cf. Windelband, History of Philosophy, p. 474, n. 1. 



20 Hume's treatise and inquiry. 

for publication, than when writing the Inquiry. On 
the former occasion, he withdrew certain obnoxious 
portions, including the argument against miracles, in 
order that the work might give *'as little offence as 
possible;"'^ but on the latter, he had no such pru- 
dential scruples when dealing with religious ques- 
tions." It is true, Hume had, in general, much re- 
gard for public opinion; but he rarely manifested 
any concern for what he called "superstition," or 
religious bigotry. 

The omissions mentioned above are partly counter- 
balanced by the introduction of two new sections— x 
and xi— which deal with miracles and the practical 
consequences of natural religion, and by the trans- 
ferrence of the discussion on liberty and necessity 
from the second book of the Treatise of Human 
Nature to the Inquiry, where it follows immediately 
the treatment of necessary connection, and forms a 
complete section by itself, section viii. These addi- 
tions to the later work serve to illustrate the practical 
application of Hume's theoretical principles within 
the sphere of morality and religion. And there can 
be little doubt that one of the chief aims of the author 
in making these changes was to induce people to 
examine his philosophical system. He hoped, by 
the publication of the Treatise, to obtain much fame 
on account of the originality, boldness, and practical 
tendencies of his philosophy of human nature. ' Nat- 
urally, therefore, he was greatly disappointed when 
the book failed to make a noise in the world. But he 

1 Burton, Life, 1, pp. 63, 64. 

2 Cf. My Own Life; Burton, Life, I, p. 239. 

3 Cf. My Oton Life; Burton, Life, I, pp. 64, 108. 



INTRODUCTION. 21 

resolved to profit by his adverse experience. Soon 
after the publication of the first two volumes, he sent 
to Hutcheson, for perusal, the manuscript of the third 
volume, the Treatise of Morals. And in the course of 
his reply to Hutcheson 's suggestions and friendly 
criticism he significantly observed:^ "I have many 
other reflections to communicate to you ; but it would 
be troublesome. I shall therefore conclude with 
telling you, that I intend to follow your advice in 
altering most of those passages you have remarked as 
defective in point of prudence; though, I must own, 
I think you a little too delicate. Except a man be in 
orders, or be immediately concerned in the instruction 
of youth, I do not think his character depends upon 
his philosophical speculations, as the world is now 
modelled ; and a little liberty seems requisite to bring 
into the public notice a book that is calculated for few 
readers." Some years later, when writing the In- 
quiry, the author astutely availed himself of "a little 
liberty," in order to bring the book into public notice. 
It has been commonly thought that Hume mani- 
fested one of the few weak points in his character by 
making a high bid for that notoriety for which his 
soul craved, when in the Inquiry he introduced the 
sections dealing with miracles, providence, and im- 
mortality.^ But the author of the Treatise of Hu- 
man Nature, in this criticism of popular religious con- 
ceptions, had a much deeper object in view than the 
attainment of mere notoriety. He wished to call the 
attention of readers to the importance of his new 

1 Burton, Life, I, p. 114. 

^ Cf. Selby-Bigge, Humes Enquiries, Introd. ; Huxley, Hume, 
p. 11; III, p. 36. 



22 Hume's treatise and inquiry. 

system. That the scheme was well conceived, and 
that it was eminently snecessful, later philosophical 
discussion has most abundantly testified. 

The transference of the section on liberty and 
necessity from the second book of the Treatise of 
Human Nature to its appropriate place in the Inquiry 
— directly after the section on necessary connection — 
may have been prompted somewhat by logical con- 
siderations. But it seems indubitable, because of the 
new mode of treatment which the subject received, 
that the change was made chiefly for the purpose of 
stimulating public curiosity. For the most important 
alteration, in the later presentation, is the greater 
prominence given to the difficulties that, on any theory 
of the will, whether deterministic or libertarian, arise 
in the sphere of philosophy of religion. This dis- 
cussion, along with those on miracles, providence, and 
immortality, Hume undoubtedly thought would at 
once arouse the indignation of "the zealots," But 
he was again grievously disappointed. In the Auto- 
biography he expressed his mortification to find, on 
his return from Italy, "all England in a ferment, on 
account of Dr. Middleton's Free Enquiry," while 
his own performance was "entirely overlooked and 
neglected." Yet in the long run, the author of the 
philosophy of human nature was not far wrong in 
his calculation. He had accurately gauged some of 
the fundamental qualities of mankind. In a few 
years, his bookseller informed him that his "former 
publications (all but the unfortunate Treatise) were 
beginning to be the subject of conversation," and that 
new editions of them were demanded.^ "Answers 

^ My Own Life. 



INTRODUCTION. 23 

by Reverends, and Right Reverends, came out two or 
three in a year"; and Hume found, "by Dr. War- 
burton's railing, that [his] books were beginning to 
be esteemed in good company." Since then, no 
writer on miracles has neglected to mention the great 
skeptic ; while to refute him has been the ardent aim 
and earnest endeavor of every Christian apologist. 
§ 5. Mode of Procedure.— It is now only necessary 
to add a word with regard to method, in order to con- 
clude this introduction. I propose to proceed top- 
ically, treating each subject of importance separately, 
and following as closely as possible the order of the 
earlier work. In the topical treatment I shall state, 
first, the doctrine of the Treatise on the point in 
question ; secondly, the position of the Inquiry on the 
same subject, noting the differences of view that may 
exist, whether in the way of omission, addition, or 
modification ; and thirdly, indicate, as far as possible, 
the reasons for the changes that appear in the later 
work. 



CHAPTER II. 

Hume's aim, subject-matter, and method. 

§ 6. Hume's Aim.— We now enter upon the sub- 
ject proper of our investigation, viz., the relation of 
Hume's earlier philosophical principles to his later, 
as they are set forth respectively, in the Treatise, and 
in the Inquiry. The first question to determine is 
that of aim. Accordingly, in the present chapter, we 
shall compare the introduction to the Treatise of Hu- 
man Nature with the first section of the Inquiry. 
Throughout, it will be borne in mind, of course, that 
the prefatory remarks in the Treatise are an introduc- 
tion to the science of man,^ while the first section of 
the Inquiry is an introduction to only one part of the 
science of man, the theoretical part. Much light will 
thus be thrown on some of the differences that ex- 
ist between these two forms of statement, that is, be- 
tween the general introduction to the science of man, 
and the introduction to the theoretical part of the 
science of man.^ 

In the advertisement to the earlier work, Hume 
said that his ''design" was sufficiently explained in 
the introduction. Nevertheless, his readers have 
never arrived at any general agreement regarding 
what his design, or purpose was. Thus Mackintosh 
asserts:^ " [Hume] aimed at proving, not that nothing 

1 1, p. 303. 

2 Cf. p. 7, above. 

^Dissertation on the Progress of Ethical Philosophy, p. 137; 
cf. Reid's Works, I, p. 183. 

24 



AIM, SUBJECT-MATTER, AND METHOD. 25 

was known, but that nothing could be known;— from 
the structure of the understanding to demonstrate, 
that we are doomed for ever to dwell in absolute and 
universal ignorance." Priestley:^ ** According to 
[Hume's] own very frank confession, his object was 
mere literary reputation. It was not the pursuit of 
triith, or the advancement of virtue or happiness." 
Stirling i^ ''Hume's final aim, of course, is the de- 
struction of what is to him superstition." Huxley:^ 
"The aim of the KritiJc der reinen Vernunft is essen- 
tially the same as that of the Treatise of Human 
Nature, by which indeed Kant was led to develop 
that critical philosophy with which his name and 
fame are indissolubly bound up." Stewart:* 
" [Hume's] aim is to establish a universal skepticism, 
and to produce in the reader a complete distrust in 
his OAvn faculties." It is unnecessary to multiply 
examples further. Diversity of view on this question 
is doubtless due as much to objective differences in 
the two accounts of Hume's philosophy, as to sub- 
jective differences in the various interpreters. 

The key to the solution of this problem is to be 
found only in Hume's life. From his ''earliest in- 
fancy ' ' he exhibited a strong inclination to books and 
letters. When a youth he amused himself in leisure 
hours writing on psychological, ethical, or literary 
subjects.^ At eighteen, he experienced for a few 

^Letters to a Philosophical Unieliever, p. 125; cf. Morris, 
British Thought and Thinkers, p. 238. 

2 Mind, Vol. IX, p, 533 ; cf. Revue Philosophique, Vol. XII, 
p. 121. 

^ Hume, p. 58; cf. Pfleiderer, Empirismus u. Skepsis, p. 109. 

* Collected Works, I, p. 437; cf. McCosh, Hist, of Scottish 
Phil, pp. 153, 154. 

6 Burton, Life, I, p. 13. 



26 Hume's treatise and inquiry, 

months the ecstasy of "philosophical conversion," 
"There seemed to be opened up to me," he writes,^ 
"a new scene of thought, which transported me be- 
yond measure, and made me, with an ardor natural 
to young men, throw up every other pleasure or 
business to apply [myself] entirely to it," Hume 
now felt that he had a message to deliver to the world. 
He would work a revolution in philosophy or moral 
science, similar to that which Bacon had effected in 
physical science. He resolved on the plan of writing 
a complete system of philosophy, as Spencer did a 
little more than one hundred years later. This proj- 
ect he also carried out, although— since the Treatise 
did not "meet with success"— not without some modi- 
fications, and not quite so thoroughly as he had at 
first intended. For instead of the volumes on politics 
and criticism, which were to form part of the Treatise 
of Human Nature, there appeared only the moral and 
political essays, two essays on religion, and a few 
fragmentary pieces. 

Like every philosopher who has a new doctrine 
to propound, Hume discovered that the current 
theories of knowledge were exceedingly defective.^ 
At the age of twenty-three he wrote :^ "Every one 
who is acquainted either with the philosophers or 
critics, knows that there is nothing yet established in 
either of these two sciences, and that they contain 
little more than endless disputes, even in the most 
fundamental articles." In the introduction to the 
Treatise, he expresses himself no less strongly. Re- 
garding philosophy, he says :* ' ' Principles taken upon 

1 Op. cit., I, p. 31, 

2 Of. Kant, Kritik d. r. Vernunft, Vorrede. 
• Burton, Life, I, p. 31, * P. 305. 



AIM, SUBJECT-MATTER, AND METHOD. 27 

trust, consequences lamely deduced from them, want 
of coherence in the parts, and of evidence in the 
whole, these are everywhere to be met with in the 
systems of the most eminent philosophers, and seem 
to have drawn disgrace upon philosophy itself. ' ' And 
concerning the sciences, he asserts :^ ' ' Even the rabble 
without doors may judge from the noise and clamor, 
which they hear, that all goes not well within. There 
is nothing which is not the subject of debate, and in 
which men of learning are not of contrary opinions. 
The most trivial question escapes not our controversy, 
and in the most momentous we are not able to give 
any certain decision." 

Hume now proposes to improve this unfortunate 
state of things by means of his philosophy of human 
nature, or, as he frequently calls it, the science of man. 
In a similar manner had Bacon, Locke, Descartes, 
and many other thinkers hoped, with the aid of phi- 
losophy, to advance the sciences and extend knowl- 
edge. "I cannot forbear," says Hume,^ "having a 
curiosity to be acquainted with the principles of moral 
good and evil, the nature and foundation of govern- 
ment, and the cause of those several passions and in- 
clinations, which actuate and govern me. ... I am 
concerned for the condition of the learned world, 
which lies under such a deplorable ignorance in all 
these particulars. I feel an ambition to arise in me 
of contributing to the instruction of mankind, and of 
acquiring a name by my inventions and discoveries," 
All the sciences have a definite relation to human 
nature; in short, human nature is their "capital or 
center. "^ " There is no question of importance, whose 
, iP. 305. 2 P. 550. P. 307. 



28 Hume's treatise and inquiry. 

decision is not comprized in the science of man ; and 
there is none, which can be decided with any cer- 
tainty, before we become acquainted with that sci- 
ence." If, therefore, we obtain a mastery of the 
science of man, "we may extend our conquests over 
all those sciences, which more intimately concern hu- 
man life, and may afterwards proceed at leisure to 
discover more fully those, which are the objects of 
mere curiosity. "^ "In pretending, therefore, ' ' he con- 
tinues, "to explain the principles of human nature, 
we in effect propose a complete system of the sciences, 
built on a foundation almost entirely new, and the 
only one upon which they can stand with any se- 
curity." Although Hume here makes extravagant 
claims for his philosophy, there cannot be any doubt 
with regard to his meaning. He will write a treatise 
that will include the sciences of "Logic, Morals, 
Criticism, and Politics" ; a treatise that will not only 
serve as a handmaid to all the other sciences, but that 
will at the same time comprehend ' ' almost everything, 
which it can any way import us to be acquainted 
with, or which can tend either to the improvement 
or ornament of the human mind. "^ For he believes 
he has discovered the "new medium,"^ by which truth 
may be established.* This thought not only implied 
a brilliant generalization, but also indicated, in a 
striking manner, that practical turn of mind so char- 
acteristic of the philosophers of Scotland. 

In the Inquiry, Hume 's aim, on a cursory examina- 

1 P. 307. 2 lUd. 3 Burton, Life, I, p. 31. 

* Cf. Aikins, The Philosophy of Hume, p. 35 ; McCosh, Hist. 

of Scottish Phil., pp. 153, 154; Petzholtz, Die Hauptpunhte 

d. H. Erkenntmslehre, p. 8j Falckenberg, Hist, of Modern 

Phil, p. 221. 



AIM, SUBJECT-MATTER, AND METHOD. 29 

tion, seems to be similar to that of the Treatise of 
Human Nature.^ In the first section, the author re- 
gards knowledge as being in the same imperfect con- 
dition as formerly. The "abstruse philosophers," 
he says,^ "think it a reproach to all literature, that 
philosophy should not yet have fixed, beyond contro- 
versy, the foundation of morals, reasoning, and crit- 
icism ; and should for ever talk of truth and falsehood, 
vice and virtue, beauty and deformity, without being 
able to determine the source of these distinctions," 
Hume does not make such large claims, however, on 
behalf of his philosophy of human nature as he did 
in the earlier work, probably because of disappoint- 
ment at the failure of the Treatise to call forth public 
notice.^ As early as 1740, in a letter to Hutcheson, 
he said:* "I am apt in a cool hour to suspect, in gen- 
eral, that most of my reasonings will be more useful 
by furnishing hints, and exciting people's curiosity, 
than as containing any principles that will augment 
the stock of knowledge, that must pass to future 
ages." Even in passages of the Treatise, he mani- 
fested an apprehension that he would not obtain the 
degree of success he hoped for. He did not expect to 
make "many proselytes" to his view of belief;^ he 
did not doubt that his sentiments on necessary connec- 
tion would be treated by many of his readers as ' ' ex- 
travagant and ridiculous";'' finally, after bewailing 
"the wretched condition, w-eakness, and disorder of 

1 Cf. Pillon, Psycliologie de Hume, p. II. 

2 P. 4. 

^Cf. Burton, Life, 1, pp. 105, 108; Hume, Hist, of England, 
VII, p. 359. 

* Burton, Life, I, p. 118. 

^P. 416. 6 Pp. 461, 468. 



30 Hume's treatise and inquiry. 

the faculties," together with 'Hhe impossibility of 
amending or correcting" them, he made the doleful 
confession:^ ''This sudden view of my danger [of 
perishing on the barren rock, on which I am at pres- 
ent], strikes me with melancholy; and as it is usual 
for that passion, above all others, to indulge itself ; I 
cannot forbear feeding my despair, with all those 
desponding reflections, which the present subject fur- 
nishes me with in such abundance. ' ' Hume, no doubt, 
did not mean all these forebodings to be taken lit- 
erally. Yet, since the reception given the Treatise 
justified his fears to the full, it is not surprising to 
find a tone of dejection in the introduction to the 
Inquiry. "Abstruse thought and profound re- 
searches," he says,^ "[nature prohibits], and will 
severely punish, by the pensive melancholy which they 
introduce, by the endless uncertainty in which they 
involve you, and by the cold reception which your 
pretended discoveries shall meet with, when communi- 
cated. ' ' 

Nevertheless, as before, Hume thinks that the sci- 
ence of man "has its peculiar merit," and that it will 
contribute to "the entertainment, instruction, and 
reformation of mankind."^ After distinguishing 
theoretical philosophy from practical, he states that 
the theoretical philosophers "think themselves suffi- 
ciently compensated for the labor of their whole lives, 
if they can discover some hidden truths, which may 
contribute to the instruction of posterity."* He as- 
serts that, by employing the maxim of the priority of 

iP. 544; cf. Burton, Life, I, p. 105. 
2 P. 6. 3 p. 3, 

«P. 4; cf. IV, p. 253. 



AIM, SUBJECT-MATTER, AND METHOD. 31 

impressions to ideas, "we may reasonably hope to 
remove all disputes, which may arise," concerning 
the nature and reality of ideas.^ And he maintains 
that the science of man will facilitate the advancement 
of all other sciences ; for theoretical philosophy is sub- 
servient to practical. The latter without the former, 
"can never attain a sufficient degree of exactness in 
its sentiments, precepts, or reasonings"; and a spirit 
of accuracy carries "every art or profession" nearer 
its perfection, rendering it "more subservient to the 
interests of society." Hence, the genius of philos- 
ophy gradually diffuses itself "throughout the whole 
society, ' ' and bestows ' ' a similar correctness on every 
art and calling. "^ 

Thus far, although Hume, for the reason already 
mentioned, is not so sanguine as formerly in his man- 
ner of expression, there is no difference noticeable be- 
tween the aim of the Treatise of Human Nature and 
the aim of the Inquiry. Presently, however, a new 
aspect of the question emerges. It is objected, in the 
later work, that "metaphysics," that is, "abstruse 
philosophy," is not "properly a science," and that 
"a considerable part of metaphysics" arises either 
from * ' the fruitless efforts of human vanity, ' ' or from 
"the craft of popular superstitions."^ To this the 
author answers that for the same reason the study of 
human nature is the more necessary, "The only 
method of freeing learning, at once, from these ab- 
struse questions, is to inquire seriously into the nature 
of human understanding, and show, from an exact 
analysis of its powers and capacity, that it is by no 
means fitted for such remote and abstruse subjects. 
iP. 17. 2 Pp. 6, 7; cf. p. 24. »P. 8. 



32 Hume's treatise and inquiry. 

We must submit to this fatigue, in order to live at 
ease ever after : And must cultivate true metaphysics 
with some care, in order to destroy the false and 
adulterate. ' '^ And he concludes the section with the 
hope that he may be able to "undermine the founda- 
tions of an abstruse philosophy, which seems to have 
hitherto served only as a shelter to superstition, and 
a cover to absurdity and error. ' ' 

Because of the remarks just quoted, and on account 
of changes in the subject-matter of the Inquiry, many 
of Hume's interpreters have thought that the aim 
of the later work is essentially different from that of 
the earlier. Thus Aikins asserts:^ "The investiga- 
tion of Human Nature was undertaken in the hope 
that through a knowledge of its principles a founda- 
tion for all the sciences could be laid."— "The In- 
quiry, on the other hand, was written after the bit- 
terly disappointing reception given the Treatise had 
quenched much of Hume's zeal for philosophy and 
driven him to work in other fields of literature. . . . 
Now not only was he addressing a popular audience, 
but he had lost enthusiasm for his subject, and the 
Enquiry concerning Human Understanding suggests 
more than a suspicion that Hume's interest in it was 
more anti-theological than psychological. The intro- 
duction speaks, not of the foundation to be laid for 
all the sciences by the study of human nature, but of 
popular superstitions to be driven from their shelter 
among the brambles of metaphysics."^ Brede* and 
some other critics have expressed a similar view on 
this question. 

1 P. 9. 2 Phil, of Eume, p. 35. ^Ilid., p. 49. 

*Der UnterscMed d. Lehren H., pp. 45 S.; cf. Seth, Scottish 
Philosophy, p. 69. 



AIM, SUBJECT-MATTER, AND METHOD. 33 

Respecting the change in subject-matter a general 
explanation was given in the preceding chapter ;^ fur- 
ther reference to the topic will be made presently.'^ 
It should be observed noAv, that those writers who 
profess to perceive a difference in the aim of the two 
works neglect to note that, in the concluding section 
of the Treatise, Hume supplements the statement of 
his aim given in the general introduction. The aim 
in the introduction, as previously remarked,^ is the 
general aim of the whole work, the Treatise of Human 
Nature; that aim as modified in the last section of 
Book I is the particular aim of the Treatise, the book 
with which we are dealing. In order, therefore, to 
obtain a correct idea of the aim of the Treatise, it is 
necessary to take account of the concluding section. 
Here Hume, after stating that the sentiments of 
curiosity and ambition are "the origin" of his phi- 
losophy, asserts:^ "But even suppose that this curios- 
ity and ambition should not transport me into specu- 
lations without the sphere of common life, it v/ould 
necessarily happen, that from my very weakness I 
must be led into such inquiries. It is certain, that 
superstition is much more bold in its systems and 
hypotheses than philosophy; . . . Since, therefore, 
it is almost impossible for the mind of man to rest, 
like those of beasts, in that narrow circle of objects, 
which are the subject of daily conversation and action, 
we ought only to deliberate concerning the choice of 
our guide, and ought to prefer that which is safest 
and most agreeable. And in this respect I make bold 
to recommend philosophy, and shall not scruple to 

iPp. 16-22. «Pp. 36^1. 3p, 24. 

*Pp. 550, 551; cf. IV, p. 406. 
3 



34 Hume's treatise and inquiry. 

give it the preference to superstition of every kind or 
denomination." In these sentences, it is true, the 
author does not explicitly state that one of the ob- 
jects of the Treatise was to overthrow superstition. 
Nevertheless, such an object is evidently implied, both 
here and in other passages of the book. Thus he says 
that, "if we are philosophers, it ought only to be upon 
skeptical principles, and upon an inclination, which 
we feel to the employing ourselves after that man- 
ner. "^ 

It may be objected, perhaps, that the aim of the 
later work still appears to be somewhat different from 
that of the earlier. For in the Treatise^ Hume re- 
peatedly repudiates metaphysics, while in the first 
section of the Inquiry he seems to advocate the pur- 
suit of this study. "But may we not hope that phi- 
losophy," he asks,^ "if cultivated with care, and en- 
couraged by the attention of the public, may carry 
its researches still farther, and discover, at least in 
some degree, the secret springs and principles, by 
which the human mind is actuated in its operations 1 ' ' 
The rejection of a subject of examination, he con- 
tinues, on the ground that it does not lie "within the 
compass of human understanding, "is not desirable; 
nor ought to be embraced too rashly." The differ- 
ence here pointed out, however, is only apparent. 
Hume, in the Inquiry,* disavows all truly metaphys- 
ical investigations as fully as in the Treatise. "When 
he expresses the hope that philosophy may discover, 
"at least in some degree, the secret springs and prin- 
ciples, by which the mind is actuated in its opera- 

iP. 550; cf. pp. 308, 309; IV, pp. 27, 28. 
2 Pp. 321, 392, 460. 3 Pp. 11, 12. 

*Cf. pp. 8, 13, 27, 28, 30, 66, "133. 



AIM, SUBJECT-MATTER, AND METHOD. 35 

tions, " he does not expect to discover the nature of 
ultimate or metaphysical principles, but only to 
arrive at an explanation of such principles as "cus- 
tom," or "the association of ideas." These prin- 
ciples he occasionally speaks of as ultimate or original 
qualities of human nature, and he tries— "at least in 
some degree" — to account for the mode of their oper- 
ation.^ 

The fact that Hume, in the introduction to the 
Treatise, reprobates metaphysics, and yet in the first 
section of the Inquiry argues at considerable length 
in defence of metaphysics, is easily explained. He 
uses the term in two very different senses. There is 
the true metaphysics, and the false. The former 
merely means "profound reasonings," or "every 
kind of argument, which is any way abstruse";^ 
while the latter means rationalistic, or transcendental 
speculations. Rationalistic speculations Hume uni- 
versally condemns; but "profound reasonings" he 
defends in the Treatise as well as in the Inquiry.^ 
Several of the arguments which he adduces in the 
later work, in favor of philosophical studies, appeared 
in the earlier, either in the general introduction, or 
in the concluding section. For instance, in the intro- 
duction to the Inquiry he commends the study of 
"metaphysics" as a means of "safe and harmless 
pleasures"; but in the conclusion to the Treatise he 
asserted:^ "These sentiments [of curiosity and am- 
bition] spring up naturally in my present disposition ; 
and should I endeavor to banish them, by attaching 

lOf. I, pp. 321, 330; IV, p. 37. 
«I, p. 30Gj IV, p. 6. 
^Cf. I, pp. 306-309 j IV, pp. 6-9. 
*P. 550. 



36 Hume's treatise and inquiry. 

myself to any other business or diversion, I feel I 
should be a loser in point of pleasure ; and this is the 
origin of my philosophy." 

While it is readily admitted that the references, 
in the later work, to the overthrow of superstition, 
are more definite and emphatic than are those in the 
earlier ; it must, at the same time, be pointed out that 
they seem to have been made but incidentally. Hume, 
in the Inquiry, when still grieving over the sad fate of 
the Treatise, entered on a special defence of meta- 
physics, or "profound reasonings." In the course of 
the discussion it is asserted, as a serious objection to 
these studies, that "a considerable part of meta- 
physics" arises either from ''the fruitless efforts of 
human vanity, ' ' or from ' ' the craft of popular super- 
stitions." Whereupon, the author naturally replies 
that there is then so much the more reason why 
"true" metaphysics should be cultivated with care, 
in order that superstition, or "the false and adulter- 
ate," may be destroyed. That the defence of meta- 
physics is fuller and more systematic in the Inquiry 
than in the Treatise, is doubtless due largely to the 
unfavorable reception accorded to the earlier work. 
Besides, as has been remarked, the first section of the 
Inquiry is an introduction to the theoretical part of 
the science of man, while the corresponding section 
of the Treatise of Human Nature is an introduction 
to the science in general; and this, Hume probably 
thought, did not require any special defence or 
apology. 

The aim of the Treatise, therefore, is found upon 
closer examination to be essentially the same as that 
of the Inquiry, viz., to explain the nature or char- 



AIM, SUBJECT-MATTER, AND METHOD. 37 

acter of human knowledge, through an investigation 
of the contents of the individual mind, in order to 
advance science on the one hand, and to overthrow 
"superstition" and rationalistic philosophy on the 
other.^ It is true, the aim is stated in a different 
manner in the two works ; but for this difference, rea- 
sons have already been assigned.^ 

In all probability, however, it will still be objected 
that the aim of both works can hardly be the same, 
since the Inquiry contains much new material of a 
polemical character. The force of the objection dis- 
appears at once, when one reflects that Hume had 
already published part of this material in Book II 
of the Treatise of Human Nature,^ and that he in- 
tended to publish the remainder— all, or at least the 
larger portion— in Book I, but withdrew it at the 
last moment, lest it should give ''too much offense" 
as the world was then "disposed."* If it be eon- 
tended further, that the aim of both works is not 
identical, since much old material is omitted in the 
Inquiry; the obvious reply is, that these omissions 
do not necessarily affect Hume 's theory of knowledge. 
Moreover, the essential aim of an abridged work may 
be exactly the same as that of the complete work. But 
finally, it will no doubt be said that the character and 
tone of the two books are fundamentlly different, and 
that the aim must, therefore, be different also. The 
premises in this case are admitted, but not the con- 
clusion—except in part, and here is where the ground 

1 Cf. Pillon, Psychologie de Hume, p. iii. 

»Pp. 28-31, above. 

'Cf. p. 22, above. 

♦Burton, Life, I, pp. 63, 64. 



38 Hume's teeatisb and inquiey. 

for debate really lies. A few words of explanation, 
however, will make the matter clear. 

In writing a book, an author may be said to have, 
in general, two kinds of aims, intrinsic or universal, 
and extrinsic or individual. The intrinsic aim is the 
desire of the writer to advance knowledge, or promote 
truth, happiness, etc., by means of the principles or 
ideas expressed. The extrinsic, individual, or ac- 
cidental aims are various, such as desire for money, 
fame, notoriety, public good-will, recreation, personal 
pleasure, etc. At one time the intrinsic aim may 
predominate, at another, the extrinsic. Hume, when 
writing each work, was undoubtedly influenced by 
both these classes of motives. And whether the in- 
trinsic or the extrinsic aim predominated, when he 
was writing the Inquiry, cannot easily with positive 
certainty be determined. It is recognized, of course, 
by all competent critics, that in the Treatise the in- 
trinsic aim predominates. But on the other hand, 
it may be conceded that in the Inquiry the extrinsic 
aims, formally at least, appear to preponderate. 

The above admission will perhaps be regarded as 
a virtual surrender of the point in issue. Such, how- 
ever, it is by no means intended to be. It is made 
merely for the sake of clearness and precision, con- 
stituting as it does a new basis for further discussion. 
Hume's primary aim in the Treatise, as has been re- 
peatedly stated, was the presentation of a true theory 
of knowledge which would be of service to science, 
and which would help to overthrow rationalistic meta- 
physics. And his primary aim in the Inquiry, as 
has now been acknowledged, was, possibly, external 
conditions or individual circumstances. But from 



AIM, SUBJECT-MATTER, AND METHOD, 39 

these propositions to draw the conclusion that the 
aim of the Inquiry is essentially different from that of 
the Treatise, before examining at all the ground of 
the difference in the statement of these two aims, 
would not only be premature, but unjustifiable. The 
difference in aim, as above conceded, between the 
two works, is really but apparent, and admits of easy 
explanation. One of Hume's chief objects, in writ- 
ing the Inquiry, was to call the attention of the public 
to the system of philosophy expounded in the Treatise. 
In a letter to Home, in 1742, he said that there was a 
demand for the Essays— Moral and Political. ''I am 
. . . told that Dr. Butler has everywhere recom- 
mended then ; . . , They may prove like dung with 
marl, and bring forward the rest of my philosophy, 
which is of a more durable, though of a harder and 
more stubborn nature. ' '^ Then he wrote the Inquiry, 
partly at least, for the purpose of helping the Essays 
to bring forward the Treatise. Hence this motive, 
although nominally extrinsic, is properly speaking in- 
trinsic, since Hume's ultimate object was to carry the 
reader beyond the abridged account of his system to 
the complete exposition. And it must finally be con- 
cluded that Hume, when writing the Inquiry, was 
actuated more by intrinsic than by extrinsic motives ; 
for in reality the former were paramount, although 
it may seem that formally the latter predominated. 

Furthermore, it may be observed that the primary 
intrinsic aim of both Avorks is exactly the same, viz., 
the presentation of a true theory of knowledge which 
might be of service to science,- and which would sub- 

i Burton, Life, I, p. 143. 

2 Cf. Orr, David Hume, p. 85. 



40 Hume's teeatise and inquiry. ' 

vert rationalistic metaphysics. That this aim is 
sought in a different way in each book is due to 
the different circumstances under which the books 
were written; and from these changes in circum- 
stances there naturally resulted corresponding changes 
in the extrinsic aims. Hume gave a detailed and 
abstract account of his theory of knowledge in the 
Treatise, because he expected to establish a great 
philosophical reputation by means of the work. In 
this object he had apparently failed. Then he ap- 
pealed from the tribunal to the forum, and presented 
in a popular manner the more easy and interesting 
parts of his system. Also, before publishing the 
Treatise, he withdrew some portions of it and modified 
others, in order that it might give ' ' as little offence as 
possible," because he intended to present a copy to 
Dr. Butler, and hoped to obtain the applause of the 
learned world. The learned world, however, took 
but little notice. Hence, in the Inquiry, he restored 
these omitted portions, and expressed his views on 
religious questions more freely and less charitably. 
He thought thereby to rouse the learned world up a 
little, and after a while, indeed, he succeeded. 
Hume had now attained to a position such that hos- 
tility from theological quarters tended rather to ad- 
vance his fame than to impede it. Besides, opposi- 
tion from those whose good opinion one does not 
expect to win is often preferable to blank indifference. 
In short, the inevitable conclusion is, that the in- 
trinsic aim of both works is paramount, and also 
identical; but that the extrinsic aims are different. 
This is equivalent to saying that Hume's real object, 
in his philosophical writings, was ever the same; but 



AIM, SUBJECT-MATTER, AND METHOD. 41 

that the means which he adopted for the realization 
of this end varied at different times, according as the 
circumstances seemed to require. This view, it may- 
be added, is in perfect accord with the character qf 
the man. Though firm in his rights, steadfast in his 
principles, inflexible in his purposes, Hume was es- 
sentially a child of experience, ever willing to learn 
wisdom from the eternal laws of nature, and to con- 
form, in accidentals, to the ways of the world. The 
distinction just made between Hume's intrinsic and 
extrinsic aims, although in itself simple enough, is 
one that has never before been made. Yet by means 
of it, the obscurity which has so long prevailed upon 
the question, whether the aim of the Inquiry is the 
same as that of the Treatise, is entirely removed. 

§7. Hume's Subject-matter. — By subject-matter 
here is meant, not the particular topics which are 
dealt with in the Treatise and Inquiry, but rather 
Hume 's philosophy, in its general characteristics, as it 
is presented in these two works. The philosophy of 
human nature, the science of man, or moral philos- 
ophy—all of which terms the author uses sj'^nonym- 
ously— comprises all the more important sciences 
which deal with human life or conduct. It is divided 
into theoretical philosophy, and practical;^ or more 
specifically, into logic, morals, politics, and criticism.^ 
Both these modes of classification are given in the 
Treatise, but only the former in the Inquiry, probably 
because in his later writings Hume did not intend 
to present his complete system. The science of man 
is, therefore, on the one hand, a psychological account 

» IV, p. 3 ; cf. II, p. 235. 
« I, pp. 303, 307. 



42 Hume's treatise and inquiry, 

of human knowledge, and on the other, a scientific 
treatment of motives and conduct, based on the theory 
of knowledge previously expounded. As already 
stated/ it is only the first of these divisions of the 
science that comes within the scope of this work. 

The philosophy of human nature, as contained in 
the Treatise and Inquiry, rests on two fundamental 
principles, the sensational origin of ideas, and the 
representational theory of knowledge. Hume pro- 
fesses to establish the validity of the former prin- 
ciple by means of proofs;^ but the latter he simply 
assumes, accepting it without question from preceding 
philosophers. He is thus, at the outset of his specula- 
tions at least, an empiricist, and an idealist. While 
he is a phenomenalist, he does not hold consistently 
to either the cruder or the finer form of the hypothesis 
of cosmothetic idealism. Occasionally he speaks as if 
knowledge were a tertium quid interposed between the 
mind and the external object, but again, as if it were 
merely a modification of the mind itself. He accepts 
implicitly Locke's definition of knowledge— the per- 
ception of the agreement or disagreement of two ideas. 
Hence he is equipped with what he regards as the 
only true criterion of certainty.^ And since he as- 
sumes that the only objects of knowledge are states 
of consciousness, or impressions, ideas, and relations, 
he regards the science of man as a propaedeutic to all 
the other sciences. Of course, Hume does not always 
hold consistently to his assumption respecting the 
subjectivity of knowledge. He conforms himself, 

1 P. 4. 2 cf. p. 51, below. 

s Cf. I, pp. 311, 324, 371; IV, pp. 13, 51, 124, 125. 



AIM, SUBJECT-MATTER, AND METHOD. 43 

sometimes consciously, sometimes unconsciously, to 
"the manner" of thinking and speaking with "the 
vulgar. ' '^ It may be further noted that the Treatise 
and Inquiry contain two very important, and at the 
same time different elements, one logical, the other 
psychological. The logical element is negative in 
tendency, and professes to prove, from an examination 
of the human understanding, that certain supposed 
kinds of knowledge— for example, metaphysics— are 
impossible. The psychological element, on the other 
hand, is positive in tendency, and undertakes to show, 
in a similar manner as before, that certain kinds of 
knowledge— for example, "a mental geography"— 
are possible. It is sufficient to remark here that both 
these elements, as well as the conflict between them, 
stand out more prominently in the Treatise than in 
the Inquiry. The significance of this difference will 
be dealt with later.^ 

There has been considerable discussion on the ques- 
tion, whether Hume was perfectly sincere in adopting 
from Locke and Berkeley the fundamental principles 
of his system. Mamiani^ affirms that it is a great 
misconception to think that the author of the Treatise 
was serious. And Hamilton* asserts that Hume 
merely took up the conclusions of his predecessors, 
without indorsing them, and demonstrated the im- 
possibility of establishing a philosophical system on 
a theory of pure empiricism. On the other hand, 

II, pp. 491, 499; IV, p. 29 n. 
«Pp. 117-125; 127-132; 299-304. 

3 Simon, Berkeley's Principles of Human Knowledge, App. 
II, p. 194. 
* Discussions, p. 87. 



44 Hume's treatise and inquiry. 

Seth declares:^ ''There is no reason to doubt that 
. [Hume] accepted in perfect good faith the funda- 
mental positions from which he argued." The chief 
reasons for the former opinion are: (1) The ab- 
surdities into which Hume's reasoning sometimes led 
him; and (2) the numerous admissions which he made 
in the Treatise regarding the probable ineffectiveness 
of his arguments.^ When these considerations, how- 
ever, are weighed against the serious statements of 
the author in the introduction to his work, in the 
appendix, and in several letters,^ there can be no 
doubt that the balance of evidence is in favor of the 
latter view.* Moreover, it is well known that Eeid 
held for many years, in perfectly good faith, essen- 
tially the same philosophical presuppositions as his 
skeptical antagonist. In a letter to Hume in 1763, 
he made the following significant admission:^ ''Your 
system appears to me not only coherent in all its 
parts, but likewise justly deduced from principles 
commonly received among philosophers." The sub- 
sequent remark of Seth,® that "in refusing to look 
upon Hume's system as a substantive or serious ac- 
count of the nature of things, we may thus fairly 
claim to be taking him at his own valuation," is ob- 
viously open to criticism. We cannot regard one, nor 
a few of Hume 's statements as a just valuation of his 
system of philosophy, without taking account of the 

^Scottish Phil, p. 68; cf. Knight, Hume, p. 130; Mill, Ex- 
amination of Hamilton, p. 554; Orr, David Hume, pp. 94-101. 
2(7/=. pp. 416, 461, 468, 544. 
'Burton, Life, I, pp. 31, 62, 65, 108. 
* Cf. Mind, Vol. XI, p. 269. 
5 Burton, Life, II, p. 155. 
^Scottish Phil., p. 70. 



AIM, SUBJECT-MATTER, AND METHOD. 45 

circumstances under which they were made, and with- 
out giving due consideration also to counter state- 
ments, when such, of a directly opposite nature and 
tendency, appear in his writings. Orr's estimation, on 
this question, is the true one. ' ' There is abundant 
evidence," he says,^ "that Hume regarded himself as 
an original discoverer in philosophy. He speaks re- 
peatedly and complacently of 'my system.' He is 
confident that he has succeeded where others had 
failed in establishing the theory of human nature 
upon a just foundation." 

§ 8. Hume's Method.— y^YalQ the subject-matter 
of Hume's philosophy is but vaguely defined in 
the title of his chief work— J. Treatise of Human 
Nature,— XhQ method is clearly indicated — "An at- 
tempt to introduce the experimental method of rea- 
soning into moral subjects." Nevertheless, differ- 
ent opinions have been expressed concerning it.^ 
The view of Morris,^ viz., that Hume's method is 
"the method of empirical psychology," derived 
from that of "physical inductive science," is sub- 
stantially correct. For by experimental method 
Hume meant simply the scientific or inductive method, 
as this is now generally understood. It is no aston- 
ishing reflection to consider, he says,* "that the ap- 
plication of experimental philosophy to moral sub- 
jects should come after that to natural at the distance 
of above a whole century; since we find in fact, that 
there was about the same interval betwixt the origins 

J David Hume, p. 104. 

2 Cf, Long, Ueher Hume's Lehre v, d. Ideen u. d. Substance, 
p. 37; Hodgson, The Philosophy of Reflection, I, p. 239. 

3 British Thought and Thinkers, pp. 247, 253. 
*P. 308; cf. IV, p. 174. 



46 Hume's teeatise and inquiry. J 

of these sciences; and that reckoning from Thales 
to Socrates, the space of time is nearly equal to that 
betwixt My Lord Bacon and some late philosophers in 
England,^ who have begun to put the science of man 
on a new footing, and have engaged the attention, and 
have excited the curiosity of the public. ' ' He thinks 
it evident, * ' that the essence of the mind being equally 
unknown to us with that of external bodies, it must 
be equally impossible to form any notion of its powers 
and qualities otherwise than from careful and exact 
experiments, and the observation of those particular 
effects, which result from its different circumstances 
and situations."^ Hume thus includes, under the 
term experimental method, observation of one's own 
mind, and observation of other minds, human and 
animal, in so far as the nature of mental states and 
processes can be subjectively perceived, interpreted 
by conduct, or disclosed by a study of physiology. 
He employs not merely the ordinary method of em- 
pirical psychology in its two aspects, subjective and 
objective, but also, to some extent, the comparative, 
genetic, and historical methods.^ "The experimental 
method" is not to be confused, of course, with the 
method of experimentation as now employed in what 
is commonly called the "new psychology." For 
although Hume resorted at times to experiment, in 
order to confirm, or to illustrate his reasoning, and 

1 " Mr. Locke, my Lord Bhaftsbury, Dr. Mandeville, Mr. 
Hutchinson, Dr. Butler, etc." — The space of time is not so 
nearly equal as Hume would represent, being from Thales 
(640 or 625) to Socrates (469) 171 (or 156) years, and 
from Bacon to Locke 71 years. 

2 P. 308. 

3 Cf. I, pp. 364, 365, 468, 469. 



AIM, SUBJECT-MATTER, AND METHOD. 47 

declared that "all our perceptions are dependent on 
our organs, and the disposition of our nerves and 
animal spirits,"^ he was after all but a worthy fore- 
runner of the modern school of experimental psy- 
chologists. 

In the Inquiry also, Hume emphasizes the experi- 
mental or scientific method. In the first section he 
says that "the only method of freeing learning" from 
abstruse metaphysical questions "is to inquire seri- 
ously into the nature of human understanding, and 
show, from an exact analysis of its powers and capac- 
ity, that it is by no means fitted for such remote and 
abstruse subjects,"^ It will be noted, however, that, 
in addition to this statement, he asserts :^ ' * Accurate 
and just reasoning is the only catholic remedy, fitted 
for all persons and all dispositions; and is alone able 
to subvert that abstruse philosophy and metaphysical 
jargon, which, being mixed up with popular super- 
stition, renders it in a manner impenetrable to care- 
less reasoners, and gives it the air of science and 
wisdom." Also in the twelfth section he affirms:* 
"To begin with clear and self-evident principles, to 
advance by timorous and sure steps, to review fre- 
quently our conclusions, and examine accurately all 
their consequences; though by these means we shall 
make both a slow and a short progress in our systems ; 
are the only methods, by which we can ever hope to 
reach truth, and attain a perfect stability and cer- 
tainty in our determinations." These last two pas- 
sages, if interpreted with strict literalness, are incon- 
sistent with Hume's former statements; for here he 
seems to abandon the inductive method of the seien- 

iP. 498. 2 p. 9. 3 p. Ibid. *P. 123. 



48 Hume's teeatise and inquiry. 

tists, and to adopt the deductive method of the phi- 
losophers. But the truth of the matter is that the 
"accurate and just reasoning" which is spoken of in 
the first passage, is conversant with matters of fact; 
and the "clear and self-evident principles" which are 
referred to in the second, are arrived at by means of 
induction. Although Hume, in both works,^ seemed 
to make certain assumptions, and then reasoned from 
these according to the deductive method, yet in most 
cases, these assumptions are ultimately based, im- 
plicitly at least, on observation and experiment. In 
the Inquiry, the author did not discard, nor even sub- 
ordinate his experimental method. For the result of 
his investigation is but a "mental geography, or de- 
lineation of the distinct parts and powers of the 
mind";^ that is, a description of impressions and their 
copies, in their coexistence and succession. Like- 
wise, without adopting any of the distinctive methods 
of experimental psychology, he introduced, as in the 
Treatise, a few experiments in the psychology of sen- 
sation^ in order to prove, or to illustrate his argu- 
ments.^ 

It is obvious, therefore, that Hume adopts the scien- 
tific method in both works. The deductive element 
of this method although perhaps not more generally 
employed in the later work than in the earlier, is more 
fully recognized in the first section of the Inquiry than 
in the introduction to the Treatise of Human Nature. 
This change may be explained, in part, on psycholog- 
ical grounds ; Hume at first expected to obtain extra- 
ordinary results from the use of his experimental 

1 Cf. I, pp. 324, 326, 339; IV, pp. 13-15, 124, 125. 

2 P. 10; cf. pp. 15, 17. 
Cf. IV, pp. 15, 124, 125. 



AIM, SUBJECT-MATTER, AND METHOD. 49 

method. But the change is probably due, in the 
main, to the difference in subject-matter of the two 
introductions; the one being an introduction to the 
science of man, the other an introduction to the 
theoretical part of the science. Hence, when the an- - 
thor afterwards takes up the discussion of practical 
philosophy, in the Inquiry concerning the Principles 
of Morals, he again emphasizes the importance of the 
inductive element. Regarding the nature of moral 
distinctions he asserts •} "As this is a question of fact, 
not of abstract science, we can only expect success, 
by following the experimental method, and deducing ' 
general maxims from a comparison of particular in- 
stances." Hume designated the Treatise of Human 
Nature, "An attempt to introduce the experimental 
method of reasoning into moral subjects," because in 
the work he employed the inductive method of the 
natural scientists, rather than the deductive method 
of the rationalistic philosophers. This method he 
followed in the Inquiry in a like manner, and sub- 
stantially to the same extent as in the Treatise. 
1 IV, p. 174. 



CHAPTER III. 

PERCEPTIONS: THEIE NATURE, AND CAUSE. 

§ 9. The Nature and Classification of Perceptions. 
—Although Hume, in his psychology, adopted an 
atomistic view of mind, he did not carry out his 
analysis of the concrete phenomena of consciousness 
sufficiently far to enable him to distinguish between 
the purely psychological standpoint, and the epistemo- 
logical. The ultimate elements of consciousness are, 
for him, not merely structural, but also functional. 
While together they constitute the stream of thought, 
each one separately has meaning, it knows. Failure 
to perceive the true significance of this fact has been 
one of the chief reasons why, on the one hand, the 
merits of Hume 's system have seldom been fully real- 
ized, and why, on the other, the philosophy of human 
nature has been subjected to much irrelevant and 
inane criticism. 

In the Treatise, all mental phenomena are called 
perceptions. These are the only objects of human 
knowledge.^ Although conjoined, they are not con- 
nected, they all are distinct and separable; that is, 
perceptions generally do not exist separately, but they 
all may be thought of as existing separately, and con- 
sequently, may all exist as distinct and separate en- 
tities.^ They are complex, or simple, according as 

1 Cf. pp. 311, 324, 327, 339, 371, 396, 408, 466, 483, 493, 503, 
518, 523, 558. 

2Cf. pp. 319, 326, 343, 370, 376, 381, 388, 456, 463, 495, 518, 
540, 558, 559. 

50 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 51 

they can, or cannot be resolved into simpler elements.^ 
Perceptions form two general classes, impressions, 
and ideas. Impressions are always the first to appear 
in the mind. Of this Hume gives two proofs c^ (1) 
''Every simple impression is attended with a corre-* 
spondent idea, and every simple idea with a corre- 
spondent impression." (2) ''Wherever by any ac- 
cident the faculties, which give rise to any impression, 
are obstructed in their operations [or when the organs 
of sensation have never been put in action to produce 
a particular impression] , not only the impressions are 
lost, but also their correspondent ideas." Hence it 
follows that all ideas are copies of impressions. Sim- 
ple ideas differ from their corresponding impressions 
only through their less degree of force, vivacity, or 
liveliness.=^ But complex ideas differ also in some 
other— although not important— respects from the 
complex impressions from which they were derived; 
for instance, they are less perfect or complete, and 
their details are more confused.* With regard to 
force or liveliness, impressions and ideas merge into 
each other, or blend by imperceptible degrees, and 
consequently, at times, cannot be distinguished by 
introspection.^ Impressions are of two kinds, those 
of sensation, and those of reflection. Impressions of 
sensation are those that arise "in the soul originally, 
from unknown causes," by means of the senses, also 
sensations of "heat or cold, thirst or hunger, pleasure 
or pain." Impressions of reflection "arise mostly 

iP. 312; cf. p. 328. 

2 p. 314. 

3(7/. pp. 311, 312, 327, 396, 452. 

*P. 313; for an apparent contradiction, see II, p. 113, 

5 Pp. 311, 421. 



52 HUME'S TREATISE AND INQUIRY. 

from ideas, ' ' but sometimes directly from impressions 
of sensation.^ They are the passions, emotions, de- 
sires, and aversions.^ There are also two kinds of 
ideas, those of sensation, and those of reflection. 
These correspond, respectively, to the two kinds of 
impressions, being copies of them.^ And since ideas 
may produce ' ' the images of themselves in new ideas, ' ' 
there arise "secondary ideas, which are images of the 
primary."* Besides the classification of ideas into 
those of sensation and those of reflection, there is an- 
other division into those of memory, and those of 
imagination. Ideas of memory differ from those 
of imagination by their fixed order of appearance in 
the mind, and by their greater degree .of force, 
vivacity, or liveliness.^ 

Probably through ignorance of continental philos- 
ophy, Hume mistakenly expresses the opinion that the 
distinction which he makes between impressions and 
ideas settles the controversy concerning innate ideas. 
Hence, he regards all impressions as innate, and all 
ideas as not innate.^ In the case of different shades 
of color, for example, blue, he admits an exception to 
his general principle that impressions always precede 
their corresponding ideas, but thinks the instance is 
so singular that the general maxim need not be 
altered.'^ True, a similar exception may be observed 
in the degrees of every distinct class of sensations— 
as indeed Hume seems to imply,^ — not only in the 

ip. 311; cf. II, p. 76. 

2 Pp. 316, 317, 324, 340. 

3 P. 317. «P. 316. 

5 P. 317, 318, 386, 387, 407, 409, 545. 
61, p. 316. 11, p. 315. 

8 1, p. 315; cf. IV, p. 16. 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 53 

sphere of color, but also in that of sound, taste, etc. 
These instances, however, strictly speaking, are only 
apparent exceptions to Hume's maxim. The differ- 
ent shades of blue are but different degrees of gray, 
or of brightness, mixed with the color tone. And" 
ideas may be increased or diminished in quantity or 
in intensity by the imagination alone. 

Of the three sections which originally dealt with 
these topics, only one appears in the Inquiry. The 
two entitled, ''Division of the Subject," and ''Of 
the Ideas of the Memory and Imagination" are en- 
tirely omitted. These omissions were doubtless made 
for the sake of brevity, and do not seem to be signifi- 
cant. Some of Hume's critics, however, have thought 
otherwise. Their views will be examined presently, 
aft«r the points on which there is no controversy have 
been stated. As in the Treatise, all mental phenomena 
are called perceptions. These are the only objects 
of knowledge.^ Perceptions are conjoined, but not 
connected; they all may be regarded as distinct and 
separate existences.^ Perceptions fall into two classes, 
impressions, and ideas. That impressions are the 
first to appear in the mind, the same two proofs are 
given as formerly.^ Hence, all ideas are copied from 
impressions, and differ from them only in degree of 
force, vivacity, or liveliness,* The exception to the 
general rule,— that all simple ideas are copies of im- 
pressions,— is noted as before in the case of color.^ 
And the controversy on innate ideas is supposed to 
be settled by the decision that all impressions are 

1 Cf. pp. 13, 15, 51, 52, 61, 64, 125. 

^Cf. pp. 27, 61, 90, 126, 134. sP. 15. 

♦Pp. 13, 14, 17; cf. II, p. 113. « P. 16. 



54 Hume's treatise and inquiry. 

innate, and all ideas are not innate.^ Thus far, 
there is complete agreement between both works; on 
some other questions there is ground for discussion. 

With regard to impressions and ideas, Hume as- 
serted in the Treatise that it is impossible at times 
to perceive, by means of introspection, the difference 
between them. "It sometimes happens, that our im- 
pressions are so faint and low, that we cannot dis- 
tinguish them from our ideas. "^ Yet in the Inquiry- 
he says :^ " [The memory and imagination] may mimic 
or copy the perceptions of the senses ; but they never 
can entirely reach the force and vivacity of the orig- 
inal sentiment. . . . The most lively thought is 
still inferior to the dullest sensation." The contra- 
diction here is only apparent. "What Hume means, 
in the latter passage, is that, under normal conditions 
and as a general rule, ' ' the most lively thought is still 
inferior to the dullest sensation." He grants that 
there are exceptions, for he asserts that when the mind 
is "disordered by disease or madness," impressions 
and ideas become "altogether undistinguishable. "* 
In the Treatise he made several statements of exactly 
similar import.^ The position of the earlier work, 
viz., that it is sometimes impossible to distinguish 
impressions from ideas by means of introspection, is 
psychologically correct. And Hume would undoubt- 
edly have expressed the same view in the Inquiry, 
had he treated the subject fully, or had he written 
solely for the philosophers and not also for the public. 

Brede® states that the distinction between simple 

iP. 17n. 2 p. 311. cf. p. 421. 

3 P. 13. *P. 13; cf. pp. 57, 124. 

5 Pp. 311, 421. 

^Der UnterscMed d. Lehren H., p. 30. 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 55 

and complex ideas is omitted in the later work, and 
thinks that this omission is due to Hume's desire not 
to emphasize the separateness of simple ideas, since 
soon after writing the Treatise the author discovered 
that he could not unite the separate ideas so easily as 
he formerly thought he could. It may be admitted 
that simple and complex ideas are not defined in the 
Inquiry. But the cause assigned by Brede is evi- 
dently not the real one. For Hume not only still 
holds that all perceptions are distinct and separate, 
and may be thought of as separate existences,^ but he 
speaks of simple and complex ideas in a manner 
implying the same distinction as that made in the 
Treatise. Incidentally, he remarks r ' ' Complex ideas 
may, perhaps, be well known by definition, which is 
nothing but an enumeration of those parts or simple 
ideas, that compose them." The difference here 
recognized, between simple and complex ideas, was 
not pointed out with the same fulness and clearness 
of detail as in the earlier work, because the author 
now aimed particularly at conciseness of statement. 
The omission is of no special significance. 

Selby-Bigge^ asserts that, in the Inquiry, the dis- 
tinction between ' ' impressions of sensation and reflec- 
tion" is omitted. But he neglects to mention that 
it is repeatedly assumed. For instance, in section 
vii Hume states :* ' ' It seems a proposition, which will 
not admit of much dispute, that all our ideas are 
nothing but copies of our impressions, or, in other 
words, that it is impossible for us to tJiink of any- 

1 Cf. I, p. 559; IV, pp. 27, 61, 90, 134. 

2 P. 51; cf. pp. 14, 15, 18. 
'Htime's Enquiries, p. xii. 

*P. 51; cf. pp. 17, 38 n., 40, 52, 53, 61, 64, 65. 



56 Hume's treatise and inquiry. 

thing, whicli we have not antecedently felt, either by 
our external or internal senses." He implies, of 
course, that the impressions and ideas of the internal 
senses are those of reflection, as distinguished from 
sensation. As he said in the earlier work,^ ' ' the idea 
of necessity" must be derived ''from some internal 
impression, or impression of reflection." In fact, 
Hume speaks of impressions and ideas of reflection 
in the same manner, and seems to attribute to them 
the same origin in both books. Thus in the Treatise 
he says •? ' ' This idea of pleasure or pain, when it re- 
turns upon the soul, produces the new impression of 
desire and aversion, hope and fear, which may prop- 
erly be called impressions of reflection, because de- 
rived from it." And in the Inquiry he asserts:^ 
" [The idea of power] is an idea of reflection, since it 
arises from reflecting on the operations of our own 
mind." Explicit treatment of impressions of reflec- 
tion was omitted, in the later work, simply for the sake 
of brevity, as was explicit mention of them often 
omitted in the earlier, for the same reason. "I shall 
only observe before I proceed any farther, ' ' remarked 
Hume in the Treatise,* "that though the idea of 
cause and effect be derived from the impressions of 
reflection as well as from those of sensation, yet for 
brevity's sake, I commonly mention only the latter 
as the origin of these ideas; though I desire that 
whatever I say of them may also extend to the 
former." It was evidently for a similar reason that 
the classification of primary and secondary ideas was 
not given in the Inquiry. For in the Treatise Hume 
said that the limitation of his maxim of ' ' the priority 
iP. 460. 2 P. 317. 3 P. 53. <P. 380. 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 57 

of impressions to ideas," arising from the recognition 
of the relation of secondary ideas to primary, was 
"an explanation" of his general principle, rather 
than ' ' an exception ' ' to it.^ 

As several writers^ have pointed out, the distinc- 
tion between the ideas of memory, and those of imagi-" 
nation is omitted in the later work. When dealing 
with this subject Hume is not only indefinite, but also 
inconsistent. In the Treatise ideas of memory are 
differentiated from those of imagination by two char- 
acteristics :^ their fixed order, and their greater force. 
At first, the former* characteristic is regarded as be- 
ing the more important, but afterwards, the latter. ° 
Again, not only may ideas of memory be so vivid, 
that they resemble impressions, and are called im- 
pressions of memory;^ but they may also degenerate 
to such a degree as to become indistinguishable from 
ideas of imagination.'^ And on the other hand, ideas 
of imagination, through repetition, may become so 
strong and vivid that they are mistaken for ideas of 
memory.^ Grimm's treatment of this question is ex- 
ceedingly plausible, and is probably the best that has 
been given. His argument, in brief, is as follows:^ 
In the early part of the Treatise, Hume regards 
memory as something self-dependent and entirely 
different from imagination. But in a later section, 

ip. 316. 

2 Cf. Pfleiderer, Empirismus u. Skepsis, p. 119 n. ; Brede, Der 
Vnterschied d. Lehren H., p. 31; Selby-Bigge, Hume's En- 
quiries, p. xii. 

a Pp. 317, 318. «P. 318. 

6 Pp. 386, 387, 545. epp. 334, 385, 387, 407. 

'P. 387. 8 Pp. 387, 416, 421. 

9 Zur Oesch. d. Erkenntnisprohlems, pp. 452, 453. 



58 Hume's treatise and inquiry. 

when he enters more deeply into the nature of knowl- 
edge of experience, and particularly of the causal 
connection of things, he develops those defects through 
which memory is almost deposed from its peculiar 
position, so that it differs from imagination only in 
degree. On account of these defects, the distinction 
between the two faculties, at first somewhat strongly 
emphasized, loses its chief worth. That may be the 
cause, therefore, why Hume in his second work 
neglects to enter upon a discussion of this subject. 
The facts are essentially as Grimm states them, and 
his conclusion is not entirely without justification. 
It is certain that Hume, when writing the Inquiry, 
was influenced by the desire to avoid the contradic- 
tions in the earlier work, and that may have been a 
reason why he neglected to give a full treatment of 
the ideas of memory and imagination. And it is prob- 
able that he perceived the impossibility of precisely 
distinguishing between these two classes of ideas, and 
therefore refrained from making the attempt within 
the compass of a popular essay. But the chief reason 
for these omissions was undoubtedly the author's de- 
sire to secure conciseness of statement; since he im- 
plicitly distinguishes between the ideas of memory 
and those of imagination, and assigns to the former, 
in contrast with the latter, the chief functions ascribed 
to them in the Treatise. "Whenever any object is 
presented to the memory or senses," he says,^ ''it 
immediately, by the force of custom, carries the im- 
agination to conceive that object, which is usually 
conjoined to it; and this conception is attended with 
a feeling or sentiment, different from the loose 
1 IV, p. 41 ; cf. pp. 13, 17, 39, 43. 



perceptions: their nature, and cause. 59 

reveries of the fancy." If Hume had revised, or 
rewritten the earlier work, instead of only portions 
of it, all the distinctions formerly made between 
memory and imagination would, in all probability, 
have been expressed in the later. Even the incon- 
sistencies that appear in the fuller statement are 
verbal, rather than real, "With care they might have 
been avoided. They cannot, therefore, fairly be re- 
garded as having any specific influence on the author 
when he wrote the Inquiry. 

Concerning the question of the nature and classifi- 
cation of perceptions, it is evident that the position of 
the two works is practically the same. On all the more 
important topics there is perfect agreement. On 
minor points, of course, owing chiefly to omissions 
in the Inquiry, there are some differences observable. 
But these are differences of treatment, not of doctrine. 
Since the distinctions which were explicitly made, in 
the earlier work, are either reasserted, or implied in 
the later, the omissions do not seem to have any 
significant bearing on Hume's philosophical position. 

§ 10. The Cause of Perceptions.— The treatment 
of the cause of perceptions is rendered somewhat diffi- 
cult, owing to the ambiguity attaching to the word 
cause. True, it was one of Hume 's main contentions, 
one of the theses which he especially aimed to prove, 
that cause means only invariable antecedent,^ ' ' Thus 
upon the whole we may infer," he declares,^ "that 
when we talk of any being, whether of a superior 
or inferior nature, as endowed with a power or force, 
proportioned to any effect ; when we speak of a neces- 

1 1, pp. 375 and ff.; IV, pp. 51 and ff. 
2 1, p. 457; cf. IV, pp. 60, 61. 



60 Hume's treatise and inquiry, 

sary connection betwixt objects, and suppose, that this 
connection depends upon an efficacy or energy, with 
which any of these objects are endowed; in all these 
expressions, so applied, we have really no distinct 
meaning, and make use only of common words, with- 
out any clear and determinate ideas." Hume, how- 
ever, was obliged to use the language at his disposal, 
and not infrequently he speaks of cause as if imply- 
ing by it producing power. Yet if the instances in 
which he seems to use cause in this sense be examined, 
it will often be discovered that the real meaning of the 
word is but invariable antecedent.^ Having defined 
what he meant by cause, he was at liberty to employ 
the terms he found most convenient for his purpose. 
No doubt, at times he found it convenient to use 
cause in an improper sense, perhaps realized that it 
was impossible to avoid such use. But in these in- 
stances he is inconsistent, and the inconsistency must 
be acknowledged. 

Concerning the cause of perceptions, that is, their 
invariable antecedent, Hume gives two different ac- 
counts.- These may be called the epistemological 
explanation, and the physiological, viz., (1) What is 
the cause of perceptions according to the philosophy 
of human nature? (2) What is the cause of percep- 
tions according to natural science ? The two questions 
require separate treatment. 

I. AYhat is the cause of perceptions according to 
Hume's system of philosophy, the epistemological ex- 
planation? In the Treatise, the author says that the 
impressions of sense arise "in the soul originally, 

1 Cf. I, pp. 316, 317, 340, 343, 385; IV, pp. 16, 17, 60, 64, 125. 
« I, pp. 313, 314. 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 61 

from unknown causes." When the impressions dis- 
appear, they leave their traces or copies; these are 
ideas of sensation— primary ideas of sensation, from 
which, in turn, may arise secondary ideas. Impres- 
sions and ideas of sensation also give rise to impres- 
sions of reflection— passions, desires, and emotions. 
These latter "are copied by the memory and imagina- 
tion and become ideas [of reflection] ; which perhaps in 
their turn give rise to other impressions and ideas. "^ 
The order of genesis then is as follows: impressions 
of sensation, ideas of sensation, impressions of reflec- 
tion, and ideas of reflection; impressions of sensation 
being the cause of ideas of sensation— sometimes also 
the cause of impressions of reflection,^— ideas of sen- 
sation the cause of impressions of reflection, and im- 
pressions of reflection the cause of ideas of reflection. 

Although the greater part of this account is omitted 
in the Inquiry, Hume's position may easily be ascer- 
tained. As in the Treatise, he distinguishes between 
impressions and ideas, and states repeatedly that all 
ideas arise from the external or internal senses, that 
is, from sensation and reflection.^ Thus there is im- 
plied the same classification of perceptions as before ; 
and the impressions of sensation and reflection are, 
respectively, the cause of their corresponding ideas. 
True, it is not explicitly stated that the impressions 
of reflection, in every instance, arise from impressions 
or ideas of sensation, Grimm* suggests that perhaps 
Hume wished thus to escape one of the contradictions 
involved in the earlier work, viz., that of making im- 

II, p. 317. 

iCf. I, p. 317; II, pp. 75, 76. 

'Cf. pp. 14, 15, 17, 40, 51, 52, 53, 61, 64, 65. 

* Zur Gcsch. d. ErkenntnisproMems, p. 589. 



62 Hume's treatise and inquiry. 

pressions of reflection causally dependent on impres- 
sions of sensation, instead of merely successive in 
time. This reason, however, does not seem to have 
been the real one. For according to Hume, causally 
dependent simply means invariably consequent. In 
this sense, Hume again, in the second book of the 
Treatise of Human Nature, regarded impressions of 
reflection, which he called secondary, as dependent 
on impressions or ideas of sensation, which he called 
original.^ And in a similar manner, in the Inquiry, 
he not only still holds that ideas are dependent on im- 
pressions—as Grimm indeed admits,^— but also that 
the impression of reflection from which the idea of 
cause is derived is dependent on impressions of sensa- 
tion.^ It seems as if the omission in the Inquiry was 
due to the author's desire for brevity of treatment, 
rather than to any change of view, or endeavor to 
avoid contradictions. 

Thus far, there has been assigned no cause of the im- 
pressions of sensation. Concerning these, in a note 
to the first section of the Treatise, Hume asserts:* 
' ' By the term of impression I would not be understood 
to express the manner, in which our lively perceptions 
are produced in the soul, but merely the perceptions 
themselves." To this statement there is nothing 
corresponding in the Inquiry, except a note on innate 
ideas, which contains the following sentence:^ *'But 
admitting these terms, impressions and ideas, in the 
sense above explained, and understanding by inflate, 
what is original or copied from no precedent percep- 

1 II, pp. 75, 76. 

2 Zur Gesch. d. Erhenntnisproilems, p. 559. 

3 Pp. 53, 62, 65; Cf. pp. 14, 15, 17, 40, 51, 52, 61, 64. 

*P. 312. «P. 17. 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 63 

tion, then may Ave assert, that all our impressions are 
innate, and our ideas not innate," Thus he implies 
that impressions are the cause of ideas, but concerning 
the cause of impressions he has nothing now to say. 
In the second section of the Treatise, however, he de- 
clares:^ "The examination of our sensations belongs* 
more to anatomists and natural philosophers than to 
moral; and therefore shall not at present be entered 
upon. ' ' In the Inquiry, there is nothing correspond- 
ing to this statement. The sentence just quoted seems 
to imply that Hume will afterwards deal with impres- 
sions. But as this investigation "belongs more to 
anatomists and natural philosophers than to moral," 
the explanation must be physiological rather than 
epistemological. Hence arises the second question, 

II. AMiat is the cause of perceptions according to 
natural science, the physiological explanation? As 
already stated, thus far, in neither work, does Hume 
assign any cause of the impressions of sensation. In 
the Treatise, he remarked that the examination of the 
impressions of sense belonged more to anatomists and 
natural philosophers than to moral, and therefore 
should not at present be entered upon. Consequently, 
when he afterwards gives a physiological explanation 
of perceptions, it might naturally be supposed that this 
explanation applies only to impressions. The treat- 
ment, however, is too general to bear this interpreta- 
tion. For when he discusses the subject in Part II, 
and again in Part IV, he speaks, not of the cause of 
impressions, but of the cause of perceptions, includ- 
ing the cause of ideas as well as that of impressions. 
In the Treatise are such passages as the following i^ 

1 P. 317. 2 p. 365. 



64 Hume's treatise and inquiry. 

"I shall therefore observe, that as the mind is en- 
dowed with a power of exciting any idea it pleases; 
whenever it dispatches the spirits into that region 
of the brain, in which the idea is placed ; these spirits 
always excite the idea, when they run precisely into 
the proper traces, and rummage that cell, which be- 
longs to the idea."— '* When we press one eye with 
a finger, we immediately perceive all the objects to 
become double. . . . But as we do not attribute a 
continued existence to both these perceptions, and as 
they are both of the same nature, we clearly perceive, 
that all our perceptions are dependent on our organs, 
and the disposition of our nerves and animal spirits."^ 
These quotations clearly indicate that the physiolog- 
ical cause of perceptions is cerebral and neural proc- 
esses—including, of course, the movements of animal 
spirits. Cerebral and neural processes are the in- 
variable antecedents of perceptions. In still another 
passage Hume declares:^ "I would answer, that we 
must separate the question concerning the substance 
of the mind from that concerning the cause of its 
thought; and that confining ourselves to the latter 
question we find by the comparing their ideas, that 
thought and motion are different from each other, 
and by experience, that they are constantly united; 
which being all the circumstances, that enter into the 
idea of cause and effect, when applied to the opera- 
tions of matter, we may certainly conclude, that 
motion may be, and actually is, the cause of thought 
and perception." It is true, he admits that this 
conclusion ** evidently gives the advantage to the 
materialists above their antagonists."^ But the ad- 

iP. 498. 2 P. 530. 3 p. 532. 



PERCEPTIONS: THEIR NATURE, AND CAUSE, 65 

mission, standing as it does against several contrary 
statements,^ has no philosophical importance.^ It 
probably occurred through the author's over zeal in 
his opposition to the "spiritualists" with their "meta-^ 
physical entities." 

Although, in the Inquiry, there is no definite answer 
given to the question concerning the physiological 
cause of perceptions, there are some statements which 
contain, at least, a partial answer. In section ii,^ 
Hume admits that, when the mind is ''disordered by 
disease or madness," ideas may "arrive at such a 
pitch of vivacity" that they are indistinguishable 
from impressions ; and in section xii,^ he implies that 
many "perceptions arise not from any thing ex- 
ternal," but from the condition of the organism, or 
from a certain state of the brain or nerves. These 
and other passages^ of like import clearly mean that 
perceptions are caused, that is, invariably preceded, 
by cerebral and neural processes, or by movements 
of the animal spirits.^ Statements confirming this 
conclusion may be found in Hume's other writings. 
In the posthumous work, the Dialogues concerning 
Natural Religion, for example, Philo asks:'^ "What 
peculiar privilege has this little agitation of the brain 
which we call thought, that we must thus make it the 
model of the whole universe % ' ' 

The conclusion now reached, viz., that the physio- 
logical cause of perceptions is cerebral processes, seems 

1 Cf. pp. 385, 546. 2 Cf. pp. 532, 533. 

3 P. 13. «P. 125, 

6 0/=. pp. 15, 55, 57, 124, 

^Cf. Huxley, Eume, pp. 76, 78; Porter, Science and Senti- 
ment, p. 311. 
' II, p. 396. 
5 



66 Hume's treatise and inquiry. 

to be inconsistent with a statement made in the sec- 
ond section of the Treatise, to the effect that impres- 
sions of sense arise in the sonl originally ''from un- 
known causes." The explanation, however, is not 
difficult. In his account of the physiological cause 
of perceptions, Hume has reference to the immediate 
cause ; hence his answer, neural and cerebral processes. 
But when the further question is raised, what is the 
ultimate cause of perceptions? he has no answer to 
give. True this question, from the philosophical point 
of view, is much more interesting than the previous 
one. But Hume does not attempt to answer it. As he 
has just said, impressions of sense arise in the soul 
originally from unknown causes ; that is, the original, 
or ultimate cause of impressions is unknown. In an- 
other passage also, he declares :^ "As to those impres- 
sions, which arise from the senses, their ultimate cause 
is, in my opinion, perfectly inexplicable by human 
reason, and it will always be impossible to decide with 
certainty, whether they arise immediately from the 
object, or are produced by the creative power of the 
mind, or are derived from the author of our being." 

In the Inquiry, almost exactly the same position is 
assumed in the first part of the twelfth section. "By 
what argument can it be proved, ' ' asks Hume,^ ' ' that 
the perceptions of the mind must be caused by ex- 
ternal objects, . . . and could not arise either from 
the energy of the mind itself, or from the suggestion 
of some invisible and unknown spirit, or from some 
other cause still more unknown to us?" It is true 
that, in the later work, the author does not draw a dis- 
tinction between the question of the immediate cause, 

II, p. 385. 2 p. 125. 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 67 

and that of the ultimate cause of impressions. Never- 
theless, this distinction seems to be implied, when he 
admits that some impressions are produced by neural 
and cerebral processes, or by the condition of the 
bodily organism;^ and when, at the same time, he 
affirms that it is impossible to tell from whence "the 
perceptions of the mind" arise.^ Thus Hume leaves 
the metaphysical question of realism and idealism un- 
determined, and asserts that it is indeterminable. It 
is a matter which lies wholly beyond the power of 
human understanding. This is the position of the 
Inquiry as well as of the Treatise. 

Before concluding the discussion, some reference 
should be made to the opinions that have been ex- 
pressed, by interpreters of Hume, regarding his doc- 
trine of the cause of perceptions. Huxley^ states 
that Hume ''fully adopted the conclusion to which 
all that we know of psychological physiology tends, 
that the origin of the elements of consciousness, no 
less than that of all its other states, is to be sought 
in bodily changes, the seat of which can only be placed 
in the brain." At the same time, he asserts that 
"Hume is not quite consistent with himself" respect- 
ing the origin of impressions of sensation,* Knight 
takes a somewhat similar view, but he is more reserved 
in the expression of it. He says:^ " [Hume] suggests 
that, for all that we know to the contrary, material 
changes may be sufficient to produce mental ones, 
but he does not teach this dogmatically." He also 
asserts that Hume is inconsistent in his treatment of 

i(7f. pp. 15, 55, 57, 124. 2 P. 125. 

*Hume, p. 74. * Hume, p. 72. 

^ Hume, pp. 143, 144; cf. Porter, Science and Sentiment, p. 
311. 



68 Hume's treatise and inquiry. 

the subject, * ' both in the Treatise, and the Inquiry. ' ' 
Webb declares:^ "But though in his psychology 
[Hume] refuses to recognise either the conceptions 
or the principles of efficient causation and essential 
substance, yet in his metaphysics he finds himself 
compelled to admit that our impressions have a cause, 
and thus to recognize with Kant the existence of a 
non-sensuous cause of our sensations." And Seth^ 
affirms that, "Hume cuts short the question of the 
cause of our impressions as a transcendental inquiry. ' ' 
Here are several different, and even contradictory 
statements. One represents that, according to Hume, 
the cause of perceptions is cerebral processes; an- 
other that the author, in both works, contradicts him- 
self; a third that the cause of impressions is a 
noumenal existence; and still another that the cause 
of impressions, being a transcendental question, is not 
investigated. The inconsistencies in these divergent 
views are accounted for, and at the same time in large 
measure removed, by the interpretation that has just 
been given. It is manifest that Hume recognizes a 
distinction between the immediate cause of perceptions 
and the ultimate cause. He distinguishes between 
the immediate and the ultimate causes of phenomena.^ 
He says of his philosophy, that it "pretends only to 
explain the nature and causes of our perceptions, or 
impressions and ideas."* He states that the cause 
of perceptions is motion, movements in the brain or 
nerves, or of the animal spirits.^ But the "ultimate 

1 Veil of Isis, p. 120; cf. pp. 87, 121. 

2 Scottish Phil, pp. 46, 48; cf. 1, p. 161; Aikins, Phil, of 
Hume, p. 44; Speckmann, Hume's metaphysische Skepsis, 
p. 24. 

s Cf. I, p. 546; IV, p. 11. *P. 368. 

6 Of. I, pp. 364, 365, 498, 515. 



PERCEPTIONS: THEIR NATURE, AND CAUSE. 69 

cause" of impressions he regards as "perfectly inex- 
plicable by human reason. ' ' That is to say, the cause 
assigned is the immediate cause, and the cause unas- 
signable is the ultimate one. ' ^ 

§ 11. Conclusion.— The more important results of 
the discussion may be summarized as follows : 

1. The Nature and Classification of Perceptions. 
According to Hume's philosophy, perceptions are the 
only objects of knowledge. All perceptions may be 
thought of as distinct and separate existences. They 
are of two kinds, impressions, and ideas. Impressions 
of sensation are the original elements, or ultimate 
facts of human experience. From these are derived 
the ideas of sensation. Impressions and ideas of sen- 
sation give rise to impressions of reflection, from 
which in turn are derived the ideas of reflection. On 
all these points the position of both works is the same, 
except that, in the Inquiry, it is not expressly stated 
—although evidently implied— that all impressions 
of reflection are utimately dependent on impressions 
of sensation. In the Treatise, it is stated that "as 
our ideas are images of our impressions, so we can 
form secondary ideas, which are images of the 
primary,"^ But this limitation of his maxim of the 
priority of impressions to ideas, Hume says, "is not, 
properly speaking, an exception to the rule so much 
as an explanation of it." The reference, naturally, 
is omitted in the briefer work. 

The classification of ideas given in the Treatise into 
simple, and complex, is omitted in the Inquiry, but 
the distinction between them is still plainly indi- 
cated.- The classification of ideas into those of 

ip. 316. 2 P. 51. 



70 Hume's treatise and inquiry. 

memory, and those of imagination is also omitted in 
the later work. Yet one of the two distinctive char- 
acteristics of ideas of memory, viz., force and vivacity, 
is expressly attributed to them; and the other, fixed 
order, is implied.^ 

2. The Cause of Perceptions. (1) The cause of 
perceptions, according to the principles of the phi- 
losophy of human nature, that is, the epistemological 
cause, has already been treated under * ' classification. ' ' 
(2) The physical cause of perceptions is motion in the 
nerves and brain, or of the animal spirits. On this 
point the position of the Inquiry seems to be identical 
with that of the Treatise, Concerning the ultimate 
cause of perceptions, Hume has no explanation to 
offer ; in both the Treatise and Inquiry, he regards it 
as unknown and unknowable. 

1 Cf. pp. 17, 41, 43. 



CHAPTER IV. 

ASSOCIATION OF IDEAS AND RESULT— COMPLEX IDEAS. 

§ 12. Association of Ideas.— Aiter it had been 
demonstrated by experimental psychology that there 
is not a special faculty of imagination, strictly speak- 
ing but rather that there are several faculties— that 
instead of imagination, there are imaginations,— it 
was natural to infer that Hume's mind was decidedly 
of the visualizing type,^ The conclusion, supported 
as it is by strong internal evidence, scarcely admits 
of doubt. Hume originated his system of philosophy 
at a very early age; and as Galton^ has shown, in 
youth the visualizing imagination is most vivid. The 
imaging activities of mind play a large part in the 
philosophy of human nature. Thus, all the objects of 
knowledge are impressions and their copies. ''What- 
ever is clearly conceived may exist; and whatever is 
clearly conceived, after any manner, may exist after 
the same manner. . . . Again, every thing which 
is different, is distinguishable, and every thing which 
is distinguishable, is separable by the imagination."^ 
It is in his treatment of relations and general ideas, 
however, that Hume's visualizing tendencies become 
most conspicuous. So long as he has to deal only 
with sense impressions, or with ideas possessing a con- 
tent that may be pictured, he has comparatively little 
difficulty. But when he treats a subject-matter that 

1 Cf. Eraser, Am. J. of Psy., Vol. IV, p. 230. 

^Mind, Vol. V, p. 301. 

»I, p. 518; cf. IV, p. 31. 

71 



72 Hume's teeatise and inquiry. 

cannot be spread out before the eye of imagination, 
he involves himself in obscurities or contradictions. 
He regards relations, at one time, as qualities of 
ideas,^ at another, as complex ideas,^ then as acts of 
comparison,^ and again as results of comparison.* 
Philosophers had concluded that the general idea 
man could represent men of all sizes only "by repre- 
senting no particular one at all."^ But Hume, car- 
ried away by his visualizing imagination, professes to 
prove, "that it is utterly impossible to conceive any 
quantity or quality, without forming a precise notion 
of its degrees."® Consequently, he concludes that 
abstract or general ideas are "in themselves, indi- 
vidual, however they may become general in their 
representation. The image in the mind' is only that 
of a particular object, though the application of it in 
our reasoning be the same, as if it were universal."^ 

Since Hume assumes that all perceptions are "dis- 
tinct and separable," and may exist separately, every 
distinct perception being "a distinct existence,"® 
one of his first problems is to show the manner in 
which ideas are connected, in order that knowledge 
may be possible. In the Treatise, this connection 
is partially effected by the faculty of memory, which 
produces an "inseparable connection,"^'' or rather a 
very strong relation,^^ between ideas remembered. But 
there are also the ideas of imagination to be related. 
If these were ' ' entirely loose and unconnected, chance 
alone would join them"; and the result would not be 

II, pp. 319, 322. 2 1^ pp. 321, 322. 

' I, p. 463. * I, pp. 352, 372. 

6 1, p. 326. 6 1, pp. 326, 327. 

"i The italics are mine. 8 1, p. 328. 

^Cf. I, pp. 319, 326, 518. "P. 321. " Cf. p. 540. 



ASSOCIATION AND COMPLEX IDEAS. 73 

knowledge, but chaos.^ Confusion happily is averted 
by means of certain principles of association, which 
relate ideas according to general laws in a regular 
and orderly manner. The principles of connection, 
or laws of association, are three : resemblance, con- 
tiguity, and cause and effect.^ 

Several critics^ have pointed out that Hume should 
have recognized only two fundamental principles of 
association of ideas, since he later reduced causation 
to a species of contiguity. It seems, however, that 
the author of the Treatise, in the section on associa- 
tion, makes causation coordinate with resemblance 
and contiguity only provisionally; for he asserts:* 
"As to the connection, which is made by the relation 
of cause and effect, we shall have reason afterwards 
to examine it to the bottom, and therefore shall not 
at present insist upon it." He arrives at his classi- 
fication inductively. And while he admits that re- 
semblance, contiguity, and causation are "neither the 
infallihle nor the sole causes" of union among ideas, 
he maintains that they are "the only general prin- 
ciples."^ 

Hume, moreover, offers a partial explanation of 
the laws of association. He calls them "natural 
relations" in contradistinction to "philosophical rela- 
tions."® He also calls them "qualities" of ideas. 
And these qualities of ideas, or uniting principles, 
he regards as "a gentle force," or "kind of Attrac- 
tion, which in the mental world will be found to have 

iP. 319. Ubid.; cf. II, pp. 82, 101. 

3 Cf . McCosh, Agnosticism of Hume and Huxley, p. 18; 
Brown, Philosophy of the Human Mind, II, p. 229; Mill, 
Analysis of the Phenomena of the Human Mind, I, p. 110. 

*P. 320; cf. I, p. 175. 6 p. 393. ep. 322. 



74 Hume's treatise and inquiry. 

as extraordinary effects as in the natural, and to show 
itself in as many and as various forms. "^ In Part 
P of the Treatise, he asserts that the cause of asso- 
ciation must be resolved into ^'original qualities of 
human nature, ' ' which he does not pretend to explain. 
But in Part 11,^ he alleges that a physiological ex- 
planation of the laws of association might be given, 
by showing "why upon our conception of any idea, 
the animal spirits run into all the contiguous traces 
[or cells, in the brain], and rouse up the other ideas, 
that are related to it." It may be noted that, in 
the opinion of Uhl,* Hume is here speaking ironically, 
perhaps with reference to Descartes. On the other 
hand, according to Morris,^ he professes his utter 
inability to explain the laws of association. The 
former view is undoubtedly incorrect; but the latter 
is true, in the sense that Hume professes his inability 
to give an ultimate explanation of these laws; he 
lays claim only to suggest a physiological explana- 
tion.^ 

In the early editions of the Inquiry, the treatment 
of association of ideas consisted largely of popular 
illustrations. These were gradually relegated to foot- 
notes, until the discussion in the text became exceed- 
ingly brief. It is now simpler, as well as briefer 
than that in the Treatise.'^ As before, Hume recog- 
nizes three principles of connection among ideas, re- 

1 P. 321. « Ibid. 3 Pp. 364, 365. 

^ Die Orundzilge d. Psychologie D. H., I, p. 29 n. ; cf. Pfleiderer, 
Empirismus u. Slcepsis, p. 121 n. 2. 

^British Thought and Thinkers, p. 248. 

6 Cf. Riehl, Der philosophische Kriticismus, I, p. 153 ; Lange, 
History of Materialism, II, p. 160. 

T Cf. Burton, Life, I, p. 286. 



ASSOCIATION AND COMPLEX IDEAS. 75 

semblance, contigruity, and cause and effect. He ad- 
raits it may be difficult to prove satisfactorily ''that 
this enumeration is complete," but thinks that "the 
more instances we examine, and the more care we- 
employ, the more assurance shall we acquire, that the 
enumeration, which we form from the whole, is com- 
plete and entire."^ Since a separate account of 
memory is not given in the Inquiry, Hume does not 
explicitly represent that faculty as a principle of 
union among ideas ; yet he does so implicitly.^ More- 
over, in conformity with his treatment of percep- 
tions,^ he does not now offer a physiological explana- 
tion of the principles of association. With the ex- 
ception of the differences just indicated, which are 
but of minor importance and are easily accounted 
for, the position of both works on the subject of asso- 
ciation of ideas is exactly the same. 

An apparent inconsistency in the two account may 
here perhaps be noted. In the Treatise* Hume said 
that resemblance, contiguity, and cause and effect 
were not the "sole causes" of union among ideas; 
but in the Inquiry,^ he says that these are "the only 
three principles of connection." The discrepancy is 
only verbal. What the author means, in the later 
work, is that resemblance, contiguity, and cause and 
effect are the only three fundamental principles of 
association. For he immediately adds, in a foot-note,® 
that "contrast or contrariety is also a connection 
among ideas." But contrast he does not regard as 
a law or principle of association, since he thinks it 
may be considered as "a mixture of causation and 
resemblance." 

1 P. 18. 2 Pp. 17, 41, 43. 3 cf. pp. G5-67 above. 

<P. 393. 5 p. 18. s lud. 



76 humb's treatise and inquiry. 

Selby-Bigge^ asserts that, "in the treatment of asso- 
ciation," in the Inquiry, "little is said about causa- 
tion as a principle of association"; while on the other 
hand, Pfleiderer^ affirms that Hume's excursion on 
association, in the later work, is too prolix. Both 
statements are substantially correct. At the con- 
clusion of the discussion, in the Treatise, Hume re- 
marked:^ "Nothing is more requisite for a true phi- 
losopher, than to restrain the intemperate desire of 
searching into causes, and having established any 
doctrine on a sufficient number of experiments, rest 
contented with that, when he sees a farther examina- 
tion would lead him into obscure and uncertain specu- 
lations. In that case his inquiry would be much 
better employed in examining the effects than the 
causes of his principle. ' ' Naturally, therefore, in the 
briefer work, after stating that the enumeration of 
the laws of association was "complete and entire," 
he continued:* "Instead of entering into a detail of 
this kind, which would lead into many useless sub- 
tilties, we shall consider some of the effects of this 
connection upon the passions and imagination ; where 
we may open a field of speculation more entertaining, 
and perhaps more instructive, than the other. ' ' Then 
followed several illustrations of his principles, as ap- 
plied in history, poetry, and the drama. This ex- 
cursion within the field of literature was transferred, 
in course of time, to foot-notes. Hence, in the early 
editions of the Inquiry the treatment of association 
is prolix, but in the later editions— omitting the foot- 
notes—it is exceedingly brief. With regard to Selby- 

1 Hume's Enquiries, p. xii. 

2 Empirismus u. Skepsis, p. 120 n. 

3 P. 321. *P. 19 n. 



ASSOCIATION AND COMPLEX IDEAS. 77 

Bigge's assertion that little is said, in the later work, 
about causation "as a principle of association," it 
may be noted that the treatment of causation, as an 
associating principle, was fuller in all the earlier, 
editions of the Inquiry than that given in the Treatise. 
As Hume, in the earlier Avork, stated that causation 
was "the most extensive"^ of the three principles of 
association, so in all the editions of the later work, 
prior to that of 1777, he affirmed that the relation- 
of cause and effect was "the strongest" of all the 
relations, and "the most instructive."^ The changes 
of treatment, in the Inquiry, were undoubtedly due 
to the author's desire to present his theory of knowl- 
edge in a popular manner; and the omissions must 
be attributed to his wish for brevity of statement. 

§ 13. Complex Ideas.— The products of the laws 
of association, or of the natural relations are com- 
plex ideas. These are philosophical relations, modes, 
and substances.^ They may be treated in their order. 

I. Philosophical Relations. It was remarked in 
the last chapter* that Hume nowhere distinguishes 
between the standpoint of psychology, and that of 
epistemology. It may be noted now that he fails in 
like manner, in his treatment of relations, to distin- 
guish between purely logical, and psychological pro- 
cesses. This is another source of ambiguity that must 
constantly be kept in mind. In the earlier work, 
the section dealing with relations is exceedingly ob- 
scure, and the several scattered references tend rather 
to befog the reader than to illumine the subject. 
Hume states that complex ideas are "the effects" of 
the natural relations. Soon, however, for natural 

»P. 320. 2 P. 19 n. »I, p. 321. <P. 50. 



78 



HUME S TREATISE AND INQUIRY. 



relations he substitutes "principles of union or co- 
hesion" among simple ideas.^ And principles of 
union, or "qualities" of objects he afterwards speaks 
of as philosophical relations.^ Philosophical rela- 
tions are distinguished from natural relations in the 
following manner.^ A natural relation is "that 
quality, by which two ideas are connected together 
in the imagination, and the one naturally introduces 
the other. ' ' A philosophical relation is ' ' that partic- 
ular circumstance, in which, even upon the arbitrary 
union of two ideas in the fancy, we may think proper 
to compare them." It will be observed that these 
definitions differ from each other only in degree. But 
Hume, in his treatment of philosophical relations, 
does not confine himself strictly to his definition. He 
speaks of philosophical relation, not only as the source 
of comparison, but also as the result of comparison,* 
and finally, as the act of comparison.^ Hence there 
appear now to be three kinds of philosophical rela- 
tions. And as one of these, the results of comparison, 

is afterwards subdivided,*^ 
there are five sorts of re- 
lations in all, — four of phi- 
losophical relations, and 
one of natural. The mat- 
ter will become clear by 
presenting this classifica- 
tion in the schematic form 
of three concentric circles. '^ 
In the inner circle are the 
natural relations, resem- 

322, 323. 3 p. 322. 

*Pp. 322, 323, 372. «?. 463. 6 P. 372. 

' Cf. Pfieiderer, Empirismus u. Skepsis, p. 128. 




iP. 321. 



Pp. 



ASSOCIATION AND COMPLEX IDEAS. 79 

blance, contiguity, and cause and effect. As these 
diminish in strength, so that they do not produce asso- 
ciations naturally, they pass to the middle circle and 
become qualities, or "particular circumstances" in- 
respect of Avhich two ideas may be compared.^ Here 
they are joined by four other "particular circum- 
stances," identity, contrariety, proportions in quan- 
tity, and degrees of quality. These seven "particular 
circumstances" are the philosophical relations that are 
purely psychological. They are "the sources" of all 
other philosophical relations,^ viz., those which are 
logical as well as psychological. This latter class is 
represented by the outer circle. It contains two sub- 
classes, acts of comparison,^ and results of com- 
parison,* corresponding respectively to the concave 
and convex sides of the circle. Finally, there is a 
twofold division of the results of comparison:^ (1) 
those that "may be changed without any change in 
the ideas," viz., identity, contiguity, and causation; 
(2) those that depend entirely upon the ideas com- 
pared, viz., resemblance, contrariety, proportions in 
quantity, and degrees of quality. 

It is not implied, of course, that Hume had the 
above classification of relations clearly in mind. Nor 
is it probable that, even if he had, he would have 
stated it explicitly. He did not possess the schematiz- 
ing faculty so characteristic of Kant. But he was 
endowed with profound psychological insight, and an 
extraordinary degree of sound common sense, which 
enabled him to seize the chief features of his problem, 
and thus to treat of relation in its most important 
stages of development. True, he did not do this 
quite consistently. The contradictions, however, are 

iP. 322. iliid. 3P. 4G3. ^Pp. 322, 372. 5 p. 372. 



80 Hume's treatise and inquiry. 

mostly verbal, apparent rather than real. And when 
these are removed, it must be conceded that his psy- 
chology of relations contains practically all the essen- 
tial elements that are yet to be met with in the most 
scientific treatment of that subject. 

Hume's doctrine of relations has often been criti- 
cised on the ground that ideas of relation are not 
copies of impressions.^ Huxley even proposed, in 
order to obviate this objection, to amend "Hume's 
primary geography of the mind," by including 
"impressions of relation" among the elementary 
states of consciousness.^ But Huxley did not have 
sufficient psychological training to enable him to be 
of any service to the Scottish philosopher on this 
occasion. Nor does the latter stand much in need 
of the proffered assistance. Hume, as indeed Seth 
admits, "does not strip his impressions quite bare 
of relations."^ He recognizes the fact of related- 
ness among perceptions.* From this the way is easy 
to "the natural relations," or laws of association. 
He recognizes the fundamental form of association, 
viz., ab — bc,^ when he speaks of "the bond of 
union" among ideas as "some associating quality."*' 
Finally, he arrives at an abstract idea of relation by 
comparing perceptions. "Since equality is a rela- 
tion," he says,'^ "it is not, strictly speaking, a prop- 
erty of the figures themselves, but arises merely from 
the comparison, which the mind makes betwixt them." 

^Cf. Introd., p. 174; Adamson, Ency. Brit., art. Hume, p. 
352; Seth, Scottish Phil., pp. 54, 55; Grimm. Zur. Gesch. d. 
Erkenntnisproblems, pp. 592, 593; Pillon, Psychologie de 
Hume, p. xiv. 

2 Hume, p. 69. '^Scottish Phil, p. 54. * I, p. 319. 

fi Cf. Titchener, Primer of Psychology, p. 131. 

«I, p. 319. 7 1^ p. 352; cf. pp. 341, 463. 



ASSOCIATION AND COMPLEX IDEAS. 81 

Thus Hume advances from the relatedness of impres- 
sions and ideas, through association and comparison 
to the abstract idea of relation. 

In the Inquiry, the section on philosophical rela-* 
tions is entirely omitted. Hume's division of com- 
plex ideas into relations, modes, and substances, be- 
ing an inheritance from Locke, is not transmitted 
to the later work; partly, because it is not essential 
to his main purpose, and partly, because he has now 
largely outgrown Locke's influence.^ For his former 
classification of complex ideas he substitutes the two- 
fold division of ''the objects of human reason or in- 
quiry, "^ viz., relations of ideas, and matters of fact, 
without stating whether the relations thus involved 
are natural or philosophical. Modes, or general 
ideas, and substances he treats incidentally; but 
philosophical relations he recognizes only indirectly/ 
without explicitly mentioning. 

Pfleiderer* suggests, as a reason for this omission 
of a treatment of philosophical relations, that the 
peculiar activity of mind betrayed by the multitude 
of relations and comparisons, in the Treatise, was 
inconsistent with Hume's theory of psychological 
atomism. The argument, however, has no weight. 
Activities of mind, that is, activities of perceptions, 
gave Hume no concern— and rightly— in his exposi- 
tion of relations. On the other hand, several am- 
biguities and some inconsistencies arose through his 
speaking of philosophical relations as the ground of 
comparison, as acts of comparison, and as results of 

1 Cf. I, pp. 308, 3423 IV, p. 17 n. 

2 P. 20. 3 Pp. 63, 64, 79. 

* Empirismus u. Skepsis, pp. 128, 129; cf. Brede, Der Vnter- 
scMed d. Lehren H., p. 33. 



82 Hume's treatise and inquiry. 

comparison, without distinguishing between psycho- 
logical relations and logical. By neglecting to treat 
this subject in the Inquiry, the author avoided 
many vexatious embarrassments. Besides, the ex- 
plicit distinction between natural, and philosophical 
relations may have been omitted because, not only is 
there no real line of separation between them, but in 
the earlier work there arose at once a confusion be- 
tween the relations of identity and resemblance, and 
also a tendency for the three natural relations to 
become indistinguishable from the three philosophical 
relations that might change "without any change in 
the ideas." Moreover, shortly after publishing the 
Treatise, Hume became more conscious than form- 
erly of the dif5S.culties involved in his system, through 
the inadequacy of relations satisfactorily to unite 
successive perceptions in consciousness, and thus ex- 
plain personal identity.^ This discovery, and like- 
wise the author's well-known desire to present the 
more important parts of his philosophy in a popular 
manner furnish additional reasons for the omission in 
the briefer work of a discussion so obscure, intricate, 
and even self-contradictory as that on philosophical 
relations.^ 

Yet this omission does not necessarily imply any 
important change in Hume's doctrine. Minor 
changes it undoubtedly signifies, but essential ones 
obviously not. Incidental references confirm this 
conclusion. Thus, in the twofold definition of cause,^ 
Plume implicitly admits a distinction between natural 

1 1, p. 559. 

2 Cf. Grimm, Zur Gesch. d. Erkenntnisprollems, pp. 458, 459, 
576; Brede, Der Unterschied d. Lehren H., pp. 32, 33. 

3 IV, pp. 63, 64, 79. 



ASSOCIATION AND COMPLEX IDEAS, 83 

relations and philosophical. And the division of 
"the objects of human reason"^ into relations of 
ideas and matters of fact, implies a distinction be- 
tween the two classes of philosophical relations ; for it^ 
corresponds in large measure, to the twofold division 
of these relations which is given in the Treatise, viz., 
into those that depend entirely upon the ideas com- 
pared, and those that may change without any change 
in the ideas. Hume now avoids all his former diffi- 
culties by substituting, for the twofold division of 
philosophical relations, the simple division of objects 
of reasoning into relations of ideas, and matters of 
fact, without explicitly stating whether the relations 
thus involved are natural, or philosophical. 

II. General Ideas. Besides philosophical rela- 
tions, the products of the laws of association are 
substances, and modes— including general ideas. The 
idea of substance will be dealt with later, along with 
that of external existence. And with regard to 
modes, the first question of interest is Hume 's doctrine 
of abstract ideas. 

Hume did not distinguish between abstract idea 
proper, and general idea, that is, between the idea of 
an attribute, and the idea of a common attribute, or 
between the idea of a part of an object, considered 
as a part, and the idea of a number of objects pos- 
sessing common qualities. Following the example of 
Locke, he used the term abstract idea for any notion 
which is the result of abstraction and generalization. 
In this way he is accountable for much of the con- 
fusion which has prevailed in philosophical discus- 
sion, and which to a certain extent still continues, 
regarding the use of the terjns abstract and general. 

nV, p. 20; cf. I, p. 423; II, p. 240. 



84 Hume's treatise and inquiry. 

It is unnecessary to go into the details of Hume's 
argument, in the Treatise, to prove that general ideas, 
so-called, are always particular. The conclusion fol- 
lows directly from his fundamental principles: All 
simple impressions are distinct existences; and all 
simple ideas are but copies of simple impressions, 
while all complex ideas are merely combinations of 
simple ideas. Hence, every idea must be determined 
in its degree ''both of quantity and quality"; that 
is, all ideas are particular.^ But although all ideas 
are particular, those that have a common name and 
are thus called general, may represent successively 
a number of individuals, "in such an imperfect man- 
ner as may serve the purposes of life." This they 
do by means of resemblance and custom.^ 

In the appendix^ Hume added a brief note on gen- 
eral ideas, merely in order to further explain his doc- 
trine, not to indicate any change of view. And in 
the Inquiry, in the few incidental references which 
he makes to this subject, he adopts the same position 
as he did in the Treatise. Thus in the twelfth sec- 
tion, after pointing out that the primary, as well as 
the secondary qualities of objects are perceptions in 
the mind, he affirms:* ''Nothing can save us from 
this conclusion, but the asserting, that the ideas of 
those primary qualities are attained by Abstraction; 
an opinion, which, if we examine it accurately, we 
shall find to be unintelligible, and even absurd. An 
extension, that is neither tangible nor visible, can- 
not possibly be conceived : And a tangible or visible 
extension, which is neither hard nor soft, white nor 
black, is equally beyond the reach of human concep- 

1 Pp. 326, 327. « P. 328. s I, p. 328 n. * P. 127. 



ASSOCIATION AND COMPLEX IDEAS. 85 

tion. Let any man try to conceive a triangle in 
general. . . . and he will soon perceive the ab- 
surdity of all the scholastic notions with regard to 
abstraction and general ideas." Again, in a note re- 
ferring to the contradictions in mathematics arising 
from the supposed infinite divisibility of quantity 
and number, he adds:^ ''It seems to me not impos- 
sible to avoid these absurdities and contradictions, if 
it be admitted, that there is no such thing as abstract 
or general ideas, properly speaking; but that all gen- 
eral ideas are, in reality, nothing but particular ones, 
attached to a general term, which recalls, upon occas- 
ion, other particular ones, that resemble, in certain 
circumstances, the idea, present to the mind." On 
the question of general ideas, therefore, the position 
of the Inquiry is identical with that of the Treatise. 
It has been much debated whether Hume 's doctrine 
of general ideas is the same in both works, and also 
whether it is the same as that of Berkeley. On the 
latter point Meinong's view,^ rather than Pfleiderer 's,^ 
is undoubtedly the more correct. Berkeley* does not 
deny absolutely that there are "general ideas," but 
only "that there are any abstract general ideas." 
Hume, on the other hand, is an ultra-Nominalist. 
On the former point, however, Meyer,^ rather than 
Meinong,^ holds the truer opinion. No change in 
Hume's doctrine of abstract or general notions is dis- 

iP. 129 n. 

i Hume-Studien, 1, pp. 218, 219; cf. Mind, Vol. Ill, p. 387. 
^ Empirismus u. 8kepsis, p. 126. 
*Fraser, Selections from Berkeley, p. 21. 
6ff. und B. Phil, der Mathematik, pp. 38, 39; cf. Mind, Vol. 
XX, p. 266. 

^ Eume-Studien, I, p. 259. 



86 Hume's tkeatise and inquiry. 

coverable in the Inquiry. Of course Hume's treat- 
ment, in the earlier work, of what he calls "a dis- 
tinction of reason," may be looked upon as a 
concession to Coneeptualism, and consequently, as 
an approach to Berkeley's position. Nevertheless, 
Grimm's statement,^ that Hume's theory of Nominal- 
ism misrepresents Berkeley's, does not seem to be 
open to criticism. The fact that the "distinction 
of reason" is not drawn in the Inquiry cannot be 
regarded as having any special significance, since in 
the later work, not only is the treatment of general 
ideas almost entirely omitted, but this omission is 
easily explained. In the Treatise, Hume gave an 
exhaustive discussion of his doctrine because, (1) he 
regarded it as ' ' one of the greatest and most valuable 
discoveries" that had been made "of late years in 
the republic of letters"; and (2) he endeavored to 
confirm it by arguments which he hoped would "put 
it beyond all doubt and controversy. "^ In the In- 
quiry, he apparently assumed that he had succeeded 
in his object,^ and consequently, thought it unneces- 
sary to discuss the question again, particularly within 
the limits of a popular essay. 

§ 14. ConcUision.— The main conclusions of the 
chapter may now be briefly stated : 

1. In the treatment of the laws of association the 
position of both works is essentially identical. In 
the Treatise, Hume discovers inductively that there 
are three general principles of association, and he 
suggests a physiological explanation of them. In the 
Inquiry, he discovers in like manner that there are 

^Zur Oesch. d. Erhenntnisprohlems, p. 461. 

2 P. 325. 3p, 127. 



ASSOCIATION AND COMPLEX IDEAS. 87 

the same three general laws; but instead of attempt- 
ing to explain their cause, he gives a popular treat- 
ment of their effects as illustrated in literature. Jn 
the earlier work, Hume remarked that nothing was" 
more requisite for "a true philosopher," than to re- 
strain the intemperate desire of searching into causes ; 
and in the later, he hoped to open up a field of specu- 
lation that would be "entertaining" and "instruc- 
tive." The change of treatment, therefore, was evi- 
dently due to his desire to popularize his doctrine. 
The omission of a physiological explanation of asso- 
ciation, in the Inquiry, is in keeping with his method 
of treating perceptions. In the briefer work, he 
does not offer any physiological explanation of the 
cause of perceptions, but implies the same view as in 
the Treatise. A similar conclusion may be inferred 
with regard to the cause of association. 

2. The products of the laws of association are com- 
plex ideas,— relations, modes, and substances. This 
classification is omitted in the Inquiry, and in its 
stead is substituted the simple division of the objects 
of reasoning into relations of ideas and matters of 
fact. Incidentally, the same view of general ideas 
is expressed as was presented at considerable length 
in the Treatise. 

The controversy on the doctrine of general ideas 
has been practically settled by experimental psychol- 
ogy. The general idea as a psychical process, or 
piece of mind, is of course particular in its existence. 
As such, however, it need not correspond to any 
particular individual thing that is included in the 
class which it represents, nor in fact to any one thing 
that exists anywhere. The error in Hume's doctrine 



88 Hume's treatise and inquiry. 

lay, not in his reasoning, but in his assumed data. He 
did not remain sufficiently true to his experimental 
method. The visualizing imagination with which he 
was endowed produced a psychological mirage, from 
the subtle illusions of which he never succeeded in 
completely freeing himself. He failed to discover: 
(1) that some minds think mainly in images, others 
in symbols; and (2) that the same mind may think 
in images, or in symbols, according as the subject- 
matter of thought is uncommon, or familiar. A pupil, 
for example, when beginning the study of algebra has 
a constant tendency to give some definite content to 
the characters employed in the reasoning; but on be- 
coming conversant with algebraic processes, he makes 
the symbols alone serve as the vehicle of thought. 
The general idea may vary from a definite mental 
image to a mere symbol. Croom Robertson struck 
the nail on the head when he remarked :^ ' ' There are 
concepts which there is no possibility of definitely 
representing and which the mind keeps hold of only by 
the help of a definite name or sign. On the other hand, 
there is a kind of image, more or less definite, which in 
certain circumstances arises in the mind as representa- 
tive of a number of resembling objects without being 
exactly representative of any of them, and which is 
thus a true concept." In every concept, the impor- 
tant factor for knowledge is not the psychological proc- 
ess, but the logical, the element of meaning. With 
this truth, indeed, Hume does not seem to have been 
wholly unacquainted, as is seen in his brief discussion 
on the "distinction of reason." But its full force, 
or true significance, he completely failed to perceive. 
1 Mind, Vol. IV, p. 553. 



CHAPTER V. 

SPACE AXD TIME. 

§ 15. Infinite Divisiiilifij.— Tart II of the Treatise 
contains Hume's doctrine of space and time. In this 
discussion dialectic skill and profound originality ai-e 
everywhere manifest. But the author's intellectual 
power is not organized. His visualizing imagination 
and erroneous presuppositions color and distort the 
argument to such an extent that this discussion, not- 
withstanding the exceedingly great merits of the ex- 
position, is the most obscure, intricate, vacillating, 
and even self-contradictory in all his philosophical 
writings. Hume indeed seems to have been somewhat 
conscious of the difficulties inherent in this part of 
his system, for he entered upon his task with unusual 
care and forethought. In the last section of Part 
I he dealt with general ideas, thus preparing the way 
for the treatment of space and time in Part II. And 
here, before grappling with his subject proper, he dis- 
posed of the minor questions concerning the infinite 
divisibility of ideas, and the infinite divisibility of 
space and time. 

Ideas, according to Hume, are not infinitely divis- 
ible, because : (1) "the capacity of the mind is limited, 
and can never attain a full and adequate conception 
of infinity"; and (2) ''whatever is capable of being 
divided in infinition, must consist of an infinite num- 
ber of parts." Hence it follows, "that the idea, 
which we form of any finite quality, is not infinitely 

89 



90 Hume's treatise and inquiry, 

divisible, but that by proper distinctions and separa- 
tions we may run up this idea to inferior ones, which 
will be perfectly simple and indivisible."^ 

It is not quite clear, however, what the nature or 
characteristics of these indivisible ideas are. For 
Hume further asserts:^ "When you tell me of the 
thousandth and ten thousandth part of a grain of 
sand I have a distinct idea of these numbers and of 
their different proportions; but the images, which I 
form in my mind to represent the things themselves, 
are nothing different from each other, nor inferior to 
that image, by which I represent the grain of sand 
itself, which is supposed so vastly to exceed them. 
What consists of parts is distinguishable into them, 
and what is distinguishable is separable. But what- 
ever we may imagine of the thing, the idea of a grain 
of sand is not distinguishable, nor separable into 
twenty, much less into a thousand, ten thousand, or an 
infinite number of different ideas." Yet on the fol- 
lowing page, he remarks: "This however is certain, 
that we can form ideas, which will be no greater than 
the smallest atom of the animal spirits of an insect a 
thousand times less than a mite." Hume's position 
seems to be this : one can form an idea about anything 
M^hatever that can be presented in imagination, no 
matter how small it may be ; but this idea itself, if of 
a very minute object, can be divided at most only a 
few times. 

Having shown that ideas are not infinitely divisible, 
Hume next endeavors to prove that space and time 
are not infinitely divisible. This is an easy task on 
the two assumptions which he makes: (1) "Whatever 

1 P. 334. 2 p. 335. 



SPACE AND TIME. 91 

ideas are adequate representations of objects, the re- 
lations ... of the ideas are all applicable to the 
objects"; and (2) "our ideas are adequate representa- . 
tions of the most minute parts of extension. ' '^ There- 
fore, since ideas are not infinitely divisible, space or 
extension is not infinitely divisible. The reasoning 
concerning the infinite divisibility of space holds also 
with respect to that of time.^ The author is now 
ready to give his derivation of the ideas of space and 
time. The two subjects may be treated separately. 
§ 16. Space.— Hume's doctrine of space and time 
is very easily misunderstood. Misconception, indeed, 
rather than interpretation, has been its common lot. 
A few quotations from expounders will serve as an 
introduction to the discussion; for the diversity of 
view among Hume's critics has much justification in 
the indefinite character of his treatement. Kiihne 
asserts:^ "Hume held, with the dogmatic metaphys- 
icians and most empiricists, space and time to be 
properties of things." Speckmann,* "Hume starting 
from empiricism, in his investigations concerning 
space and time, comes to a similar result as does Kant 
through his transcendental idealism. Space and 
time are also for him, in essence, nothing more than 
subjective forms of intuition of the sensibility." 
Ritter,^ "Kant based his standpoint [in mathematics] 
on a doctrine of space different from that of Locke 
and Hume." Brede,^ "Extension consists, . . . 

1 P. 336. ■ 2 p. 338. 

^ Ueher das Verhaltniss d. Hume'schen m. Kantischen Er- 
kenntnisstJieorie, p. 31. 

* Ueher H. metapliysische Skepsis, p. 20. 

^Kant u. Hume, p. 10. 

6 Der Vnterschied d. Lehren H., pp. 22, 23. 



92 Hume's treatise and inquiry. 

according to Hume, of a finite number of visible and 
tangible mathematical points, i. e., of points which 
have no extension in themselves, . . . but which, 
when two of them come together, do not penetrate, 
but constitute a compound body consisting of parts. ' ' 
Seth,^ "Time and space are, by [Hume's] own show- 
ing, two different manners in which perceptions are 
disposed, and in virtue of which they necessarily lose 
their character of isolated particulars. . . . They 
are relations." 

In accordance with his habitual lack of precision, 
Hume uses space and extension synonymously, also 
object and impression.^ He gives the following ac- 
count of the derivation of the idea of space: "Upon 
opening my eyes, and turning them to the surround- 
ing objects, I perceive many visible bodies ; and upon 
shutting them again, and considering the distance 
betwixt these bodies, I acquire the idea of extension, ' '^ 
Thus he regards space or extension as a quality of 
visible bodies, that is, a quality of impressions; and 
he seems to hold that the idea of extension is distance, 
or a copy of distance. But distance is a relation, as 
he himself explained formerly, "because we acquire 
an idea of it by the comparing of objects."* Hence, 
true to his philosophical principles, he immediately 
adds: "My senses convey to me only the impressions 
of colored points, disposed in a certain manner. If 
the eye is sensible of any thing farther, I desire it 
may be pointed out to me. But if it be impossible 
to shew any thing farther, we may conclude with 
certainty, that the idea of extension is nothing but 

1 Scottish Phil, p. 56. 2 Cf. pp. 341, 345. 

3 P. 340. * P. 322. 



SPACE AND TIME. 93 

a copy of these colored points, and of the manner of 
their appearance."^ Here Hume encounters a diffi- 
culty. He might have said that the idea of space is . 
distance, or a copy of distance. But now, since he 
states that the senses convey only the impression of 
colored points disposed in a certain manner, it fol- 
lows that the idea of space is a copy of color and its 
manner of appearance. In short, space or extension 
is a "compound impression" consisting of ''several 
lesser impressions, that are indivisible to the eye or 
feeling, and may be called impressions of atoms or 
corpuscles endowed with color and solidity."^ And 
the idea of space, being but a copy of extension, "con- 
sists of parts" that are indivisible, and is itself ex- 
tended.^ "The idea of space or extension is nothing 
but the idea of visible or tangible points distributed 
in a certain order."* 

Thus far, Hume has given an account of the de- 
rivation of only the particular idea of space. He 
next explains the process of transition to the general 
idea. "Wlien we have had experience of the different 
colors, and have found "a resemblance in the dis- 
position of colored points, of which they are composed, 
we omit the peculiarities of color, as far as possible, 
and found an abstract idea merely on that disposi- 
tion of points, or manner of appearance, in which they 
agree. Nay even when the resemblance is carried 
beyond the objects of one sense, and the impressions 
of touch are found to be similar to those of sight in 
the disposition of their parts; this does not hinder 
the abstract idea from representing both, upon ac- 

»P. 341. 2(7f. pp. 345, 346, 306. 

3 Gf. pp. 344, 523, 527. * P. 358. 



94 Hume's treatise and inquiry. 

count of their resemblance."^ The general idea of 
space, therefore, is the "disposition" of visual or 
tangible points, or "the manner" of appearance in 
which they agree; or as elsewhere put, the general 
idea of space is "no separate or distinct" idea, but 
merely that of "the manner or order" in which ob- 
jects exist.^ 

But the author of the Treatise does not satisfy him- 
self with a mere exposition of his theory of space. 
After presenting his doctrine, he proceeds to answer 
some objections that may be urged against it, and at 
the same time to define it more exactly. Since space 
is not infinitely divisible, what is the nature, one may 
ask, of its ultimate indivisible elements? Hume re- 
jects both the theory of mathematical points, and that 
of physical points. Each of these views is absurd.^ 
He adopts an intermediate position, and regards the 
ultimate indivisible elements of space as mathematical 
points endowed with color or solidity.* This, how- 
ever, is equivalent to saying that they are physical 
points. The author even admits, although implicitly, 
that they are such, when he asserts :^ ' ' That compound 
impression, which represents extension, consists of sev- 
eral lesser impressions, that are indivisible to the eye 
or feeling, and may be called impressions of atoms or 
corpuscles endowed with color and solidity." An- 
other essential part of Hume's doctrine is that the 
idea of space necessarily implies the existence of 
matter. The idea of pure space, or of a vacuum is 
impossible for "the idea of space or extension is 
nothing but the idea of visible or tangible points dis- 
tributed in a certain order. "^ 

»P. 341. 2 P. 346. 'lUd. 

* Cf. pp. 346, 347. 5 p. 345. 6 p. 353. 



SPACE AND TIME. 95 

§ 17. Time.— The exposition of time is similar to 
that of space. The idea of time is derived from * ' the 
succession of our perceptions of every kind, ideas as 
well as impressions^ and impressions of reflection as 
well as of sensation. ' '^ And the abstract idea of time 
"is not derived from a particular impression mixed 
up with others, and plainly distinguishable from 
them ; but arises altogether from the manner, in which 
impressions appear to the mind, without making one 
of the number. "2 Consequently, the particular idea 
of time "can plainly be nothing but different ideas, 
or impressions, or objects disposed in a certain man- 
ner, that is, succeeding each other";* and the general 
idea of time is "no separate or distinct" idea, but 
merely that of "the manner or order" in which ob- 
jects exist.* Yet, since it is impossible to have an idea 
of pure or empty time, the general idea of time is 
always represented "in the fancy by some individual 
idea of a determinate quantity and quality."^ 

§ 18. Treatment of Space and Time in tJie Inquiry. 
—In the Inquiry, there is nothing corresponding to 
Part II of the Treatise ; hence, the discussion of space 
and time is here omitted. Yet, in the twelfth section 
and appended notes, there are some statements which 
imply that practically the sam.e view of space and 
time prevails in both works.® Space and time are not 
infinitely divisible.'^ The ideas of space and time are 
derived from objects of sight and touch, by means of 
the senses.^ And it is impossible to form an idea of 
empty space, or of empty time.^ 

iP. 341. 2 P. 343. 3 P. 344. * P. 346. 5 p. 342. 
6Cf. Baumann, Die Lehren v. Ratim, Zeit u. Mathematik, 
II, p. 482. 

7 Pp. 128, 129. 8 Pp. 126, 127. » P. 127. 



96 Hume's treatise and inquiry. 

There is one remark, however, in the Inquiry, which 
is inconsistent, formally at least, with a statement in 
the Treatise, and which accordingly calls for brief 
comment. In a foot-note Hume observes:^ "What- 
ever disputes there may be about mathematical points, 
we may allow that there are physical points ; that is, 
parts of extension, which cannot be divided or less- 
ened, either by the eye or imagination." It has al- 
ready been pointed out that, in the Treatise, he re- 
jected the theory of physical points as an absurdity. 
It was inconsistent with his general maxim, "what- 
ever objects are different are distinguishable." For 
' ' a real extension, such as a physical point is supposed 
to be, can never exist without parts, different from 
each other. "^ Yet it has also been shown that, al- 
though he rejected the doctrine of physical points in 
theory, he adopted it in practice. Consequently, the 
avowal here of the system of physical points is not of 
much significance.^ It is interesting to note that, in 
the appendix, Hume had almost arrived at the same 
view. "If it be asked," he says,* "if the invisible 
and intangible distance, interposed betwixt two ob- 
jects, be something or nothing: 'it is easy to answer, 
that it is something, viz., a property of the objects, 
which affect the senses after such a particular man- 
ner.' " This statement, it is true, is not quite cor- 
rect. For an invisible, intangible distance cannot af- 
fect the senses in any manner whatever. But the im- 
portant circumstance to notice is, that what Hume 

» P. 128. i I, p. 346. 

3 Cf. Meyer, Hume u. Berheley's Phil. d. Math., p. 21, and 
n. 3; Brede, Der Unterschied d. Lehren H., p. 46. 
< I, p. 368. 



SPACE AND TIME. 97 

calls an invisible, intangible distance he really regards 
as a property of objects. 

Space and time were extremely difficult subjects 
for the author of the philosophy of human nature to 
deal with, on account of the falsity of some of his 
presuppositions. It is not surprising, therefore, that 
Part II is the most unsatisfactory division of the 
Treatise, and that it was omitted in the Inquiry. It 
is evident, however, that Hume regarded this part of 
his work as being of considerable importance, since 
he rewrote it— at least the treatment of space,— as is 
indicated by a letter to Millar in 1755. But although 
he sent the essay— "The Metaphysical Principles of 
Geometry"— to his publisher, he withdrew it before 
it was printed, because in the meantime Lord Stan- 
hope, one of the most eminent mathematicians of his 
day, convinced him that "either there was some defect 
in the argument, or in its perspicuity. ' '^ This is the 
only reason positively known why Part II of the 
Treatise, although rewritten, was never published in 
its later form. 

Before this letter to Millar became generally known, 
Avriters on Hume assigned many reasons to explain 
why Part II of the Treatise was omitted in the In- 
quiry. The argument of Brede is one of the most 
plausible, and is in substance as follows:^ "As in the 
Treatise, Hume also assumes in the Essay indivisible, 
but real, visible and tangible points as the parts of 
extension. These are distinguished from the mathe- 
matical points of the Treatise only through their name, 
physical points. On a closer investigation of this 

1 Hill, Letters of D. H., p. 230. 

' Der Unterschied d. Lehren H., p. 46. 

7 



98 hume's treatise and inquiry. 

subject Hume does not enter. Such would have been 
impossible, without a direct criticism of his former 
view, according to which physical points could be 
distinguished into different parts. And then he would 
have been involved in great difficulties, in the appli- 
cation of his axiom, that whatever is distinguishable 
is separable." It is possible that a desire to avoid 
this contradiction may have had some influence on 
Hume when writing the later work. But as Brede 
himself observes, ''the physical points" of the In- 
quiry are different only in name from ''the mathe- 
matical points" of the Treatise. It is scarcely likely, 
therefore, that in the application of his maxim, Hume 
would have found himself involved in any greater 
difficulties in the one case than in the other. Rather, 
the cause of the omission of Part II is general, not 
special. The subject is an abstract one; and Hume's 
ideas on space and time were neither perfectly clear, 
nor strictly accurate. 

§ 19. Conclusion.— It is easy, of course, as Green 
has abundantly shown, to discover inconsistencies in 
Hume's statement of his doctrine of space and time. 
For instance, space or extension is "nothing but a 
composition of visible or tangible points disposed in 
a certain order. ' '^ Upon shutting one 's eyes and con- 
sidering "the distance" between bodies, one acquires 
"the idea of extension. "^ Yet, "every idea is de- 
rived from some impression, which is exactly similar 
to it. "^ Or again, the particular idea of space is 
"nothing but a copy of . . . colored points, and of 
the manner of their appearance. ' '* The general idea 
of space is "no separate or distinct" idea, "but 
iP. 366. 2 P. 340. 3iUd. *P. 341. 



SPACE AND TIME. 99 

merely" that of ''the manner or order., in which ob- 
jects exist. ' '^ Yet, all general ideas ' ' are really noth- 
ing but particular ones, considered in a certain 
light."- But what the critics have failed to notice 
is, that Hume came remarkably near giving a valid 
and satisfactory exposition of space and time. True, 
they have admired the exceedingly ingenious manner 
in which he presented his argument. Thus if asked, 
what is space? he replies, "the manner or order in 
which objects exist." If asked, whence is the idea of 
space derived? he replies, "from objects of sight or 
touch ? ' ' And if asked, what is the idea of space ? he 
replies, "a copy" of visual or tangible points, or "the 
disposition" of visual or tangible points, according as 
the one answer, or the other, suits his purpose; the 
former answer having reference to the particular idea 
of space derived logically in accordance with his sys- 
tem, and the latter having reference to the general 
idea of space as it prevails in popular thought. The 
critics, however, have been so busily engaged in de- 
tecting fallacies, and so intent on observing inconsis- 
tencies, that they have almost entirely overlooked the 
really significant points in his doctrine. 

Hume's exposition of space and time has much 
more than plausibility to commend it. For the sake 
of brevity the discussion will be limited to the subject 
of space, as the argument, with but slight modifica- 
tions, holds equally with regard to that of time. It is 
one of the chief distinguishing traits of the philos- 
opher of Ninewells that he was the interpreter of 
actual experience, and not a prophet, nor a seer. 
That extension is an attribute of visual and tactual 

ip. 346. 2 P. 341. 



100 Hume's treatise and inquiry. 

sensations is now a common-place in psychology. 
Such also was the view of Hume; but in his termi- 
nology sensations are called impressions.^ It is true, 
"Ward, James, and a few other psychologists maintain 
that space is an attribute of all sensations. Whether 
or not this is the case depends entirely upon the 
definition of the term. Certain it is that extension 
is an object of sight and touch, that space is an as- 
pect of the real world of things. And not only was 
Hume right in holding that space is a datum of sen- 
suous experience, but he was also right in indicating 
that there is a fundamental difference between the 
individual perception of space, and the general notion. 
In this respect, he had a truer vision than had Im- 
manuel Kant. His intellectual eye was not dimmed 
by the mists of German rationalism, nor was his 
natural force abated by wrestling with noumenal ex- 
istences. Although in this instance, however, the 
open minded Scotsman had the truer psychological 
insight, it must be admitted that his visualizing im- 
agination and erroneous conception of general ideas 
misled him with regard to the exact nature of the 
difference between the particular perception of space, 
and the general notion. The essential feature of the 
latter is not the psychological element, but the epis- 
temological ; and this the author of the philosophy of 
human nature failed to perceive. For a similar rea- 
son also Hume's treatment of infinite divisibility is 
palpably defective. The particular idea of space, as 
he rightly maintained, is not capable of division to 
infinity; but the general idea of space, the funda- 
mental characteristic of which is the element of mean- 
1 P. 341. 



SPACE AND TIME. 101 

ing, is without question infinitely divisible. Of like 
nature, moreover, is Hume's treatment of a vacuum. 
He was certainly right in insisting that pure or empty 
space is never an object of perception. For what is 
ordinarily called the perception of space, the partic- 
ular idea of space, is really the perception of diffuse 
matter, bounded to a greater or less extent by objects 
of a denser quality.^ On the other, hand, however, 
he was mistaken when he asserted that the idea of 
pure space, or of a vacuum is impossible. For by 
means of abstraction one may have a general idea of 
space, an idea of pure or empty space, as the possi- 
bility of movement-sensations, or as the system of 
space relations— actual or possible— which obtains 
among external things.^ 

» Cf. Russell, Foundations of Geometry, pp. 194, 196. 
2C/=. Fullerton, Phil. Rev., Vol. X, p. 599; Nichols, The 
Psychology of Time, pp. 113, 139. 



CHAPTER VI. 

KNOWLEDGE— INTUITIVE AND DEMONSTEATIVE, 

§ 20. The Faculties of Mmd!.— The accounts of 
Hume's theory of knowledge, as presented in both 
the Treatise and Inquiry, are exceedingly perplexing. 
This is due, in large measure, to the fact that the 
epistemological terminology of his day was not ade- 
quate to the treatment of his subject-matter. At one 
time he did not properly define his terms ; at another, 
he did not consistently hold to his definitions. More- 
over, not having a sufficient number of appropriate 
terms at his command, he occasionally gave to the 
same word different, or provisional definitions, ac- 
cording as the circumstances of the case required, 
without explaining the relation of these definitions 
to one another. This is particularly true of the names 
denoting mental faculties, or sources of knowledge. 
By faculty he meant, in general, the mind acting in a 
certain way. Of those which he recognized, the more 
important are the six following: sensation, memory, 
imagination, understanding or reason, reflection, and 
instinct. 

Sensation, immediately or mediately, is the source 
of all knowledge. Wlien impressions of sense return 
as ideas, they are called memory, or imagination, ac- 
cording as they possess— as a general rule,— or do not 
possess, a certain degree of force and vivacity, and a 
certain measure of fixity of order. When the ideas 
of imagination— or of memory— lose, to a certain ex- 

102 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 103 

tent, their sense content, and are combined in new 
forms by means of comparison, abstraction, or gen- 
eralization, they become transformed into conceptions, 
and are attributed to the understanding or reason. 
Thus imagination and reason, like imagination and 
memory, differ only in degree. As Hume said,^ the 
understanding or reason is but "the general or more 
established properties of the imagination." Hence, 
memory, imagination, and reason are different stages 
of one and the same process.- Reflection sometimes 
accompanies, sometimes follows sensation, memory, 
imagination, and reason. It is in part the basis of 
instinct. 

Instinct is an indispensable factor in the philosophy 
of human nature. Of amorphous character, it plays 
many parts. It corresponds somewhat with the ele- 
ment of feeling in perceptions; it is a sentiment, or 
manner of conception. It is also closely related to 
sensation. "It seems evident," says Hume/ "that 
men are carried, by a natural instinct or preposses- 
sion, to repose faith in their senses." Moreover, in- 
stinct includes, to a greater or less extent, imagination, 
belief, habit, custom, and experiential or moral rea- 
soning. "All belief of matter of fact or real exist- 
ence," Hume affirms, in the Inquiry,* "is derived 
merely from some object, present to the memory or 
senses, and a customary conjunction between that and 
some other object. . . . This belief is the necessary 

1 1, p. 547 ; cf. IV, p. 38 n. 

* Cf. Gore, The Imagination in Spinoza and Hume, p. 74. — 
"Reason is the imagination generalized, and the imagination 
is reason particularized." 

3 IV, p. 124; cf. I, pp. 483, 548. 

<P. 40; cf. I, pp. 403, 474, 475. 



104 HUME'S TREATISE AND INQUIRY. 

result of placing the mind in such circumstances. It 
is an operation of the soul, when we are so situated, 
as unavoidable as to feel the passion of love, when we 
receive benefits: or hatred, when we meet with in- 
juries. All these operations are a species of natural 
instincts, which no reasoning or process of the thought 
and understanding is able, either to produce, or to 
prevent." Again,^ "Nothing leads to this inference 
[based on the idea of cause and effect] but custom or 
a certain instinct of our nature. ' ' And in the Treatise 
he asserts:^ '* Reason [experiential reasoning] is noth- 
ing but a wonderful and unintelligible instinct in our, 
souls, which carries us along a certain train of ideas, 
and endows them with particular qualities, according 
to their particular situations and relations. . . . 
Nature may certainly produce whatever can arise 
from habit : Nay, habit is nothing but one of the prin- 
ciples of nature, and derives all its force from that 
origin. ' ' Furthermore, instinct is a species of knowl- 
edge derived from ' ' the original hand of nature, ' ' and 
which is capable of little or no advancement.^ Finally, 
it may be regarded a;s including what are commonly 
called the ideals of reason,— goodness, beauty, truth, 
duty, etc. * ' There is a great difference, ' ' says Hume,* 
"betwixt such opinions as we form after a calm and 
profound reflection, and such as we embrace by a kind 
of instinct or natural impulse, on account of their 
suitableness and conformity to the mind. ' ' Naturally, 
therefore, instinct is superior to reason. It is the 
great guide of human life. 

iP. 131. 2 p. 471 J cf. pp. 387, 404. 

3 IV, p. 88 J cf, 1, pp. 470, 471. 

* I, p. 501 J cf. pp. 474, 475, 478, 548, 549. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE, 105 

For the sake of clearness, it is well to note that, in 
the Inquiry, Hume made less use of imagination, and _ 
more use of instinct, than he did in the Treatise. 
Many mental processes which, in the earlier work, 
were attributed to imagination are, in the later, as- 
cribed to instinct, custom, or nature. This change of 
treatment, although it does not indicate any change 
of doctrine, seems to imply a truer appreciation of the 
function of instinct. Yet it does not necessarily 
imply even this much. At most, it only rendered 
explicit in the Inquiry, what was implicit in the 
Treatise. For instinct, custom, or habit is always the 
basis or ground of the transition of imagination. The 
full significance of the change it is probably impos- 
sible to determine; for Hume used instinct, custom, 
habit, and imagination more or less interchangeably 
in both works. In the Treatise he asserted :^ ' ' When 
I consider the influence of this constant conjunction, 
I perceive, that such a relation can never be an object 
of reasoning, and can never operate upon the mind, 
but by means of custom, which determines the imag- 
ination to make a transition from the idea of one 
object to that of its usual attendant, and from the 
impression of one to a more lively idea of the other. ' ' 
Again,^ *' Reason [experiential reasoning] is nothing 
but a wonderful and unintelligible instinct in our 
souls, which carries us along a certain train of ideas, 
and endows them with particular qualities, according 
to their particular situations and relations. ' ' That is, 
reasoning is regarded equally as a transition of the 
imagination, and as a wonderful and unintelligible 
instinct. Likewise, in the Inquiry, the author stated :^ 

iP. 464; cf. p. 487. «P. 471. » P. 62 ; cf. p. 65. 



106 hume's treatise and inquiry. 

"After a repetition of similar instances, the mind is 
carried by habit, upon the appearance of one event, 
to expect its usual attendant, and to believe that it 
will exist. This connection, therefore, which we feel 
in the mind, this customary transition of the imagina- 
tion from one object to its usual attendant, is the sen- 
timent or impression from which we form the idea of 
power or necessary connection." Further,^ "We 
have no argument to convince us, that objects, which 
have, in our experience, been frequently conjoined, 
will likewise, in other instances, be conjoined in the 
same manner; and . . . nothing leads us to this 
inference but custom or a certain instinct of our 
nature." "Provided we agree about the thing," 
Hume once said, "it is needless to dispute about the 
terms. ' ' Accordingly, in the briefer wori:, instead of 
attributing certain mental processes directly to imag- 
ination, as formerly, and then indirectly to custom or 
instinct^ he often ascribed them to custom, instinct, or 
nature directly. 

§ 21. Intuitive Knowledge. — In the philosophy of 
human nature, impressions and ideas are the ultimate 
elements of knowledge. These possess certain qualities 
which constitute the ground of the three natural rela- 
tions. Natural relations are the source of the seven 
kinds of philosophical relations, also of modes and 
substances. And the philosophical relations are the 
basis of the different degrees of certainty. In Part 
III of the Treatise, Hume deals with this last problem 
under the title "Knowledge and Probability." As 
has already been stated,^ he distinguishes two classes 
of philosophical relations : those that depend entirely 

iP. 130; cf. p. 40. 2 p. 83. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 107 

upon the ideas compared, and those that may be 
changed without any change in the ideas. The 
former class-relations of resemblance, contrariety, 
degrees of quality, and proportions in number and 
quantity— constitute ''the foundation of science," and 
are objects of knowledge and certainty. The latter — 
identity, contiguity, and causation,— are the ground 
of probability.^ Knowledge is of two kinds, intuitive, 
and demonstrative; and probability also is of two 
kinds, proofs, and probability in a narrower sense.^ 
Proofs and probability will be treated in the three 
following chapters. 

Intuitive knowledge means sense and memory 
knowledge. It is based on the relations of resem- 
blance, contrariety, and degrees of quality. It arises 
immediately from the observation, or comparison of 
impressions and ideas. It does not necessarily mean 
exact, nor certain knowledge, but only that kind of 
knowledge which the mind obtains ' ' at first sight, ' ' or 
which it arrives at immediately on the perception, 
among impressions and ideas, of the relations of re- 
semblance, contrariety, or degrees of quality. Thus, 
in the Treatise, Hume asserts:^ "And though it be 
impossible to judge exactly of the degrees of any 
quality, such as color, taste, heat, cold, when the dif- 
ference betwixt them is very small; yet it is easy to 
decide, that any of them is superior or inferior to 
another, when their difference is considerable. And 
this decision we always pronounce at first sight, with- 
out any inquiry or reasoning." 

There is no specific treatment of intuitive knowl- 
edge in the later work. In the earlier, Hume, follow- 

iPp. 372, 373. 2 P. 423. »P. 373. 



108 Hume's treatise and inquiry. 

ing Locke, regarded knowledge as the perception of 
the agreement or disagreement of impressions and 
ideas; consequently, he considered the philosophical 
relations as the ground or possibility of reasoning. 
But in the Inquiry, he omitted the table of philosoph- 
ical relations, and for the classification of knowledge, 
or complex ideas, into relations, modes, and sub- 
stances, he substituted the twofold division of *'all 
the objects of human reason or inquiry," viz., rela- 
tions of ideas, and matters of fact ;^ relations of ideas 
corresponding to those philosophical relations that 
depend entirely upon the ideas compared, and matters 
of fact corresponding, in large measure, to those phi- 
losophical relations that may change while the ideas 
compared remain the same. Accordingly, under the 
former division he includes the sciences of arithmetic, 
algebra, and geometry, and in short, every affirmation 
which is either "intuitively or demonstratively cer- 
tain, ' ' and under the latter, the natural and historical 
sciences of probability.^ In Book III of the Treatise 
of Human Nature^ Hume reasserted the position of 
Book I, that resemblance, contrariety, degrees of 
quality, and proportions in number and quantity are 
the only relations which are "susceptible of certainty 
and demonstration." Although in the Inquiry* he 
thought that "the sciences of quantity and number" 
might be pronounced "the only proper objects of 
knowledge and demonstration," there is no reason to 
suppose that his view of intuitive knowledge was dif- 
ferent from that presented in the Treatise. He im- 
plies the same distinction as formerly between intui- 

1 P. 20. 2 Pp. 20, 22, 135. 

3 11, pp. 240, 241. *P. 134. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 109 

tive and demonstrative knowledge, when he says that 
"the connection" between propositions is not "intui- 
tive," if it "requires a medium."^ 

It may be imagined, perhaps, that there is some 
special significance in the substitution, in the later 
work, of the twofold division of knowledge— relations 
of ideas, and matters of fact— for the threefold divi- 
sion of the products of the laws of association, and 
for the subdivision of philosophical relations. Such, 
however, does not seem to be the case. Hume wrote 
the Treatise with Locke often in mind. But although 
he followed his master in some reduplications, cross- 
divisions, and contradictions, he endeavored to im- 
prove upon Locke's celebrated Essay. Ideas of sensa- 
tion and reflection, as the original elements of knowl- 
edge, he transformed into impressions and ideas of 
sensation and reflection. While he accepted Locke's 
definition of knowledge, and his classification of com- 
plex ideas ; instead of the four kinds of agreement and 
disagreement between ideas, as the necessary condition 
of knowledge, he put forward the seven kinds of phi- 
losophical relations. The two tables are related as 
follows : 

1. Identity and diversity. 1, 2, S. Identity, resemblance, and 

contrariety. 

2. Relation. 4, 5, 6. Contiguity or relations of 

time and place, degrees 
of quality, and propor- 
tions in number and 
quantity. 

3. Co-existence. 7. Caiise and effect. 

4. Real-existence. 

It will be observed that Hume's classification of 
1 P. 30. 



110 Hume's teeatise and inquiry. 

philosophical relations differs considerably from 
Locke's four kinds of agreement or disagreement 
between ideas; for not only has the author of the 
Treatise naturally no place for knowledge of sub- 
stance or real-existence, but his relations of identity 
and contrariety have not the same meaning as Locke 's 
agreement or disagr.eement in the way of identity 
and diversity. 

As Hume developed his system of philosophy, he 
worked gradually farther away from Locke's theory 
of knowledge, and approached, in certain respects, 
the position of Butler.^ Soon he adopted relations 
of ideas and matters of fact as a convenient classifica- 
tion of the objects of knowledge. It is one of Pat- 
ten's^ many misconceptions that this classification 
first appeared in the Inquiry. On the contrary, it 
developed step by step with the natural progress of 
the author's thought, as he proceeded from the con- 
sideration of theoretical philosophy to that of prac- 
tical. In some passages of the Treatise, for example, 
it is hinted at, or implied.^ In Book II of the Treatise 
of Human Nature it is, for the first time, explicitly 
stated. * ' Truth is of two kinds, ' ' says Hume,* ' ' con- 
sisting either in the discovery of the proportions of 
ideas, considered as such, or in the conformity of our 
ideas of objects to their real existence." And in 
Book III of the Treatise of Human Nature it is fre- 
quently employed, as in the following passage:^ "As 
the operations of human understanding divide them- 

1 Cf. Analogy, p. 3. 

2 The Development of English Thought, p. 225. 

3 Cf. pp. 394, 395, 483. 
ai, p. 223; cf. p. 227. 

511, p. 240; cf. p. 236. ; 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. Ill 

selves into two kinds, the comparing of ideas, and the 
inferring of matter of fact; were virtue discovered 
by the understanding ; it must be an object of one of 
these operations, nor is there any third operation of 
the understanding, which can discover it." The im- 
possibility of giving a popular exposition of philo- 
sophical relations, or a satisfactory treatment within 
a limited compass was probably the chief cause for 
the introduction in their stead, in the Inquiry, of the 
simple division of objects of knowledge into relations 
of ideas and matters of fact.^ 

§ 22, Demonstrative Knowledge.— Demonstrative 
knowledge is that which arises from the understand- 
ing or reason. It is based on the relations of num- 
ber and quantity. Very simple relations of number 
or quantity, such as may be observed at "one view," 
are more properly intuitive knowledge. But when 
these relations can be perceived only by means of "a 
chain of reasoning," they constitute demonstrative 
knowledge.^ The sciences of demonstration are arith- 
metic, algebra, and geometry. 

Hume's doctrine of mathematics has always been 
one of the interesting puzzles in his philosophy. It 
has been a subject of universal contention, and many 
expositions— as well as criticisms— of it have been 
given. These, however, at most have been but par- 
tially correct, and have resulted rather in contradic- 
tion and confusion, than in conviction or illumination. 
A few quotations, while exhibiting the variety of in- 
terpretation on the question, may suggest some guid- 
ing thoughts for a new solution. Masaryk asserts:^ 

» Of. pp. 80-83, above. 2 Pp. 373, 374. 

3 D. n. Skepsis u. d. WahrscheinlichJceitsrechnung, p. 6 ; cf. 
Windelband, Gesch. d. n. Phil., 1, pp. 321, 327; Kosenkranz, 



112 Hume's treatise and inquiry, 

"According to Hume, mathematics is an absolutely 
certain science, because founded on a priori prin- 
ciples." Watson,^ "The mathematical doctrine of 
Hume may be stated in these three propositions: (1) 
Mathematical judgments rest upon impressions of 
sense; (2) they are singular; (3) they are only ap- 
proximately true." Spicker,^ "We must here note 
attentively that Hume, equally with Kant, considers 
mathematics as a pure activity of thought, which 
takes place independently of all experience, and is, 
therefore, a priori certain." Stuckenberg,* "Mathe- 
matics, which Hume considered as a relation of ideas, 
is grounded by him also exclusively on experience." 
Petzholtz,* "Mathematics belongs to the sciences which 
treat of relations of ideas, whose propositions, there- 
fore, we discover through the pure activity of thought. 
. . . While Hume allows to arithmetic this uncon- 
ditioned certainty, he does not attribute such without 
reserve to geometry." Caird,^ "Hume in his earlier 
treatise attempted ... to trace back the ideas of 
mathematics to impressions of space and time: but 
the attempt led him to the denial of the objective 
validity of mathematical truth, in so far as it goes 
beyond the possibility of empirical measurement." 
Gesch. d. Kantischen Phil., p. 23; Volkelt, Erfahrung u. 
Denlcen, p. 108; Uhl, H. Stellung in d. englischen Phil., pp. 
31, 32; Ritter, Kant u. Hume, pp. 7, 9. 

^ An Outline of Philosophy, p. 357. 

^ Kant, Hume u. Berkeley, pp. 110, 117, 125; cf. Gordy, 
Hume as Sceptic, p. 1. 

" Grundproileme in Hume, p. 18; cf, I, pp. 222, 223. 

* Die HauptpunJcte D. H. Erkenntnislehre, p. 29 ; cf. Adam- 
son, Ency. Brit., art. Hume, p. 353. 

^The Critical Philosophy of I. K., I, p. 256; cf. Mahaflfy and 
Bernard, Kant's Critical Philosophy, II, p. 23, and n. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 113 

Webb,^ "As to Hume's opinion with reference to the 
a priori character of mathematics, there can be no 
intelligent diversity of opinion. . . . He abandoned 
the doctrine of the Treatise. ' ' Riehl,^ " It is erroneous 
to assert, that Hume has not doubted the validity of 
pure mathematics, since he, in the Treatise (and even 
in the Inquiry), not only doubts but positively im- 
pugns the evidence for geometry, and restricts validity 
to the abstract part of mathematics, the pure doctrine 
of quantity." Statements similar to these might be 
quoted indefinitely. They indicate great diversity in 
the answers given to the four following questions: 
(1) Is mathematics, according to Hume an a priori 
science? (2) Is it an absolutely certain science? 
(3) Is it a perfectly exact science? (4) Is there any 
difference between the respective positions of the 
Treatise and Inquiry on the three preceding ques- 
tions ? These quotations also indicate that the ground 
of their diversity is not solely subjective differences 
in the writers. The solution of the problem is to be 
sought only in a study of the objective differences that 
exist in Hume 's treatment. And the key to this solu- 
tion is the discernment that Hume, in the Treatise, 
gave three different, although not distinct or separate 
accounts of mathematics, corresponding to three stages 
of development in his doctrine. These accounts may 
be called the epistemological, the logical, and the psy- 
chological. They will be treated in their order. 

I. The Epistemological Treatment of Mathematics. 

^ Veil of Isis, pp. 101, 102 ; cf. Long, Ueher Hume's Lehre 
V. d. Ideen u. d. Suhstanz, p. 35. 

2 Der philosophische Eriticismus, I, pp. 69, 96, 97 ; cf. 
Windelband, Hist, of Phil., p. 473; Brede, Der UnterscMed d. 
Lehren H., pp. 11, 35. 



114 Hume's treatise and inquiry. 

—Hume's first account of his doctrine of mathematics 
is given in Parts II and III. The mathematical sci- 
ences, as already stated, are based on the philosophical 
relations of number and quantity. These relations, 
in turn, are based on certain qualities of impressions 
and ideas.^ Geometrical relations are modes of space. 
Arithmetical and algebraic relations are modes of 
number. Both space and number are constituted of 
simple and indivisible units. The units of space 
are mathematical points, "endowed with color" or 
' ' solidity. ' '^ But of the units of number no explana- 
tion is offered. Hume merely asserts that ' ' the unity, 
which can exist alone, and whose existence is neces- 
sary to that of all number, . . . must be perfectly 
indivisible and incapable of being resolved into any 
lesser, unity. ' '^ The idea of space is derived from the 
senses of sight and touch.* And the idea of number 
arises from the perception of objects.^ It is manifest, 
therefore, that all the mathematical sciences are em- 
pirical. 

Arithmetic and algebra Hume regards as perfectly 
exact and certain sciences, because in dealing with 
numbers, the subject-matter of these sciences, "we 
are possessed of a precise standard, by which we can 
judge of [their] equality and proportion ; and accord- 
ing as they correspond or not to that standard, we 
determine their relations, without any possibility of 
error. "^ Geometry, on the other hand, he declares 
"falls short of that perfect precision and certainty, 
which are peculiar to arithmetic and algebra, . . . 
because its fundamental principles are derived merely 

1 Cf. pp. 322, 323, 372. 2 Pp. 345^ 347. 

3 P. 338. *Pp. 340, 341, « Pp. 337, 338. « P. 374. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 115 

from appearances. ' '^ That is to say, geometry would 
be a perfectly exact and certain science, if its funda- 
mental principles, the definitions and axioms on which 
it is founded, were perfectly exact and certain. But 
these definitions and axioms are derived merely from 
the appearances of objects, and consequently, are not 
exact. Hence, the science of geometry is neither per- 
fectly exact nor certain. Yet geometry excels in ex- 
actness and certainty "the imperfect judgments of 
our senses and imagination." For although Hume 
admits that the judgments concerning geometrical 
relations are not ' ' more exempt from doubt and error 
than those on any other subject,"^ he maintains, at 
the same time, that the fundamental principles of 
geometry "depend on the easiest and least deceitful 
appearances," and therefore, "bestow on their con- 
sequences a degree of exactness, of which these con- 
sequences are singly incapable."^ 

Apparently inconsistent with the preceding account 
is a passage in which Hume asserts that "geometry 
fails of evidence" in one "single point"— its demon- 
strations for the infinite divisibility of extension, — 
but that ' * all its other reasonings command our fullest 
assent and approbation."* This latter statement, if 
taken literally, cannot be harmonized with Hume's 
general position. But the author undoubtedly meant 
that it should be understood only in a relative sense. 
For he repeatedly affirms that geometry is not an 
exact nor certain science like arithmetic or algebra, its 
first principles having been derived from the general 
appearances of objects.^ 

1 P. 374. 2 P. 353. 3 p. 374. * P. 357. 

5 Pp. 350, 353, 354, 355. 



116 Hume's treatise and inquiry. 

It may be noted, however, that if geometry dealt 
with discrete quantity, like numbers, instead of with 
continuous quantity, as is space, it would, according 
to Hume, be a perfectly exact and certain science.^ 
Arithmetic and algebra are such, because they deal 
with discrete quantity. They possess a perfect exact- 
ness and certainty, because the exact difference be- 
tween any two numbers whatever can easily be de- 
termined. The author speaks of two standards of 
certainty in geometry, one accurate, the other inac- 
curate. The inaccurate standard is the indefinite 
presentations of the senses and imagination, ' ' derived 
from a comparison of objects, upon their general ap- 
pearance, corrected by measuring and juxta-position. ' ' 
The accurate standard is the indivisible points of 
which lines and other geometrical figures are com- 
posed.2 But although this latter standard is theo- 
retically exact, it is impracticable both in science and 
in common life. If mathematicians be asked what 
they mean when they say that one line or surface is 
equal to, greater, or less than another, " [those] who 
defend the hypothesis of indivisible points," Hume 
asserts,^ "need only reply, that lines or surfaces are 
equal, when the numbers of points in each are equal ; 
and that as the proportion of the numbers varies, the 
proportion of the lines and surfaces is also varied. 
But though this answer be just," he continues, "as 
well as obvious; yet I may affirm, that this standard 
of equality is entirely useless, and that it never is 
from such a comparison we determine objects to be 
equal or unequal with respect to each other." On 
the question of the exactness and certainty of geom- 
1 Pp. 351, 374. 2 Pp. 351^ 357. 3 p, 351. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 117 

etry, he explicitly states his position as follows:^ **It 
appears, then, that the ideas which are most essential 
to geometry, viz., those of equality and inequality, of 
a right line and a plain surface, are far from being 
exact and determinate, according to our common 
method of conceiving them. ... As the ultimate 
standard of these figures is derived from nothing but 
the senses and imagination, it is absurd to talk of any 
perfection beyond what these faculties can judge of; 
since the true perfection of any thing consists in its 
conformity to its standard." 

The results of the discussion thus far may here be 
summarized. Proportions in number and quantity 
are the ground of demonstrative knowledge. But 
these proportions, like the other philosophical rela- 
tions, are derived by means of the senses. Con- 
sequently, mathematics is an empirical science. 
Arithmetic and algebra are perfectly exact and cer- 
tain sciences, since, dealing with discrete quantity, 
they possess a perfectly exact standard. But geom- 
etry, although it excels in exactness and certainty the 
inaccurate judgments of the senses or imagination, 
falls short of perfect precision, because dealing with 
continuous quantity, it lacks a perfectly exact stand- 
ard. This may be called Hume's epistemological 
treatment of mathematics. It is only one part of his 
doctrine, and is considerably modified later. 

II. The Logical Treatment of Mathematics.— In 
Part IV, the author draws the logical consequences 
of his philosophical principles, and sums up his doc- 
trine of the understanding. In the first section he 
treats of mathematics in the following manner i^ *'In 

1 P. 356; cf. pp. 348, 350, 353, 355. «P. 472. 



118 Hume's treatise and inquiry. 

all demonstrative sciences the rules are certain and. 
infallible; but when we apply them, our fallible and 
uncertain faculties are very apt to depart from them, 
and fall into error. We must, therefore, in every 
reasoning form a new judgment, as a check or control 
on our first judgment or belief ; and must enlarge our 
view to comprehend a kind of history of all the in- 
stances, wherein our understanding has deceived us, 
compared with those, wherein its testimony was just 
and true. . . . By this means all Imowledge degen- 
erates into probability. . , . There is no algebraist 
nor mathematician so expert in his science, as to place 
entire confidence in any truth immediately on his 
discovery of it, or regard it as any thing, but a mere 
probability, ... In accounts of any length or im- 
portance, merchants seldom trust to the infallible 
certainty of numbers for their security. ' ' And as no 
one will maintain ''that our assurance in a long 
enumeration exceeds probability," Hume thinks he 
may "safely affirm, that there scarce is any proposi- 
tion concerning numbers, of which we can have a 
fuller security." If "any single addition were cer- 
tain, every one would be so, and consequently the 
whole or total sum." But of course the whole is not 
certain, "Since, therefore," he concludes,^ "all 
knowledge resolves itself into probability, and be- 
comes at last of the same nature with that evidence 
which we employ in common life, we must now ex- 
amine this latter species of reasoning, and see on 
what foundation it stands." 

In every judgment concerning probability, and con- 
sequently concerning knowledge— since "all knowl- 
1 P. 473. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 119 

edge resolves itself into probability, "—there are, 
according to Hume, two sources of error and un- 
certainty, the understanding which judges, and the 
object about which the judgment is made.^ Hence, 
even "the man of the best sense and longest experi- 
ence ... [is] conscious of many errors in the past, 
and must still dread the like for the future. ' ' Hume 
contends that, because of this natural fallibility of 
the understanding, every judgment requires to be 
corrected by another judgment, this one by another 
and so on ad infinitum. Thus as "demonstration is 
subject to the control of probability," so is "proba- 
bility liable to a new correction by a reflex act of the 
mind, wherein the nature of our understanding, and 
our reasoning from the first probability become our 
objects." And he concludes again:- "When I reflect 
on the natural fallibility of my judgment, I have less 
confidence in my opinions, than when I only consider 
the objects concerning which I reason; and when I 
proceed still farther, to turn the scrutiny against 
every successive estimation I make of my faculties, 
all the rules of logic require a continual diminution, 
and at last a total extinction of belief and evidence. ' ' 
This is the logical account in Hume's treatment of 
mathematics,— or rather one might say of knowledge. 
For it has doubtless been noticed that, in following 
his order of exposition, the subject has been gradually 
broadened, until now the account applies not merely 
to mathematics but to knowledge in general. 

The foregoing passages have given rise to two dif- 
ferent lines of interpretation, neither of which is quite 
correct. According to the one, Hume distinguished 

1 P. 474. 2 Ihid.; cf. p. 475. 



120 Hume's teeatise and inquiry. 

between mathematics as a pure science and mathe- 
matics as an applied science, and maintained that the 
former possesses exact and demonstrative certainty, 
but the latter only probability. According to the 
other interpretation, Hume's doctrine of mathematics 
is the culmination of a system of absolute skepticism 
or nihilism. The former view prevails, to a consid- 
erable extent, among the German critics; the latter is 
not uncommon with the writers of the Scottish school. 
They may be examined in succession. 

Windelband affirms:^ "Mathematics is . . . the 
sole demonstrative science; and is that just because 
it relates to nothing else than the possible relations 
between contents of ideas, and asserts nothing what- 
ever as to any relation of these to a real world. In 
this way the terministic principle of Hobbes is in 
complete control with Hume, but the latter proceeds 
still more consistently with his limitation of this 
theory to pure mathematics." And Eiehl asserts:^ 
"Hume doubts not the exactness of pure, but the 
validity of applied mathematics. ' ' This position has 
been controverted by Adamson. "No question," he 
declares,^ "arises regarding the existence of the fact 
represented by the ideas, and in so far, at least, mathe- 
matical judgments may be regarded as hypothetical. 
. . . That the propositions are hypothetical in this 
fashion does not imply any distinction between the 
abstract truth of the ideal judgments and the imper- 
fect correspondence of concrete material with these 

1 History of Philosophy, p. 473 ; cf. Petzlioltz, Die Haupt- 
punJcte D. H. Erkenntnislehre, p. 29. 
2Z)er philosophische Eriticismus, I, pp. 96, 97. 
> Ency. Brit., art. Hume, p. 353. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 121 

ideal relations. Such distinction is quite foreign to 
Hume, and can only be ascribed to him from an entire 
misconception of his view regarding the ideas of space 
and time." The statement of Adamson is the more 
correct one. Not only does Hume fail to distinguish 
between ''the abstract truth of the ideal judgments 
and the imperfect correspondence of concrete material 
with these ideal relations, ' ' but he denies that this dis- 
tinction exists. "[To reason]," he says,^ ''that the 
objects of geometry, . . . are mere ideas in the mind ; 
and not only never did, but never can exist in nature, ' ' 
is ' ' absurd and contradictory. ' ' Again,^ ' ' The notion 
of any correction [in geometry] beyond what we have 
instruments and art to make, is a mere fiction of the 
mind, and useless as well as incomprehensible." 
Finally, he states conclusively:^ "It is usual with 
mathematicians, to pretend, that those ideas, which 
are their objects, are of so refined and spiritual a 
nature, that they fall not under the conception of the 
fancy, but must be comprehended by a pure and in- 
tellectual view, of which the superior faculties of the 
soul are alone capable. . . . But to destroy this arti- 
fice, we need but reflect on that principle so often 
insisted on, that all our ideas are copied from our 
impressions." At the same time, it should be ob- 
served that, somewhat in accordance with the view 
expressed by Windelband and Riehl, Hume recog- 
nized a distinction between arithmetic and algebra as 
exact and certain sciences, and the practical applica- 
tion of these sciences to concrete material. He re- 
peatedly asserted that arithmetic and algebra are 
perfectly exact and certain,* but that in practice "all 
1 P. 348. n P. 353. 3 p. 375. «Pp. 374, 472. 



122 Hume's treatise and inquiry, 

knowledge degenerates into probability."^ Further- 
more, he said:^ "In all demonstrative sciences the 
rules are certain and infallible; but when we apply 
them, our fallible and uncertain faculties are very apt 
to depart from them, and fall into error. ' ' 

Controversy on this subject has arisen owing to the 
fact that Hume neglected to give a derivation of num- 
ber. Adamson, following in the wake of Green, in- 
sists that, on Hume's fundamental principles, a de- 
rivation of number suitable to serve as a foundation 
for mathematics cannot be given. While on the other 
hand, Windelband, recognizing that Hume held arith- 
metic and algebra to be perfectly exact and certain 
sciences, erroneously concludes that mathematics is a 
pure science. The truth of the matter seems to be 
this : not only is a derivation of abstract number pos- 
sible, in accordance with the principles of empiricism, 
but so also is a derivation of abstract quantity. For 
by means of approximations, abstraction, and gen- 
eralization, the transition is not difficult from the 
perception of real lines and circles in nature to the 
ideas of perfectly straight lines and perfect circles 
corresponding to the definitions of geometry. Hume, 
neglecting to give a derivation of number, failed to 
show how arithmetic and algebra, as abstract sciences, 
are possible. Nevertheless, he rightly held that arith- 
metic and algebra are perfectly exact and certain. 
And he not only failed to give a derivation of quan- 
tity—pure or abstract quantity,— but contended that 
such could not be given, and hence mistakenly asserted 
that geometry is not an exact nor certain science. 
The position of many writers of the Scottish school, 
1 Pp. 472, 473. 2 p. 472. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 123 

that Hume 's theory of knowledge is a system of abso- 
lute skepticism, is of course unwarranted. True, in 
so far as they assert that absolute skepticism is the 
result of the strictly logical, as distinguished from the 
psychological factor in this theory of knowledge, they 
are literally correct. The author admits this himself. 
"When I proceed still farther," he says,^ "to turn 
the scrutiny against every successive estimation I 
make of my faculties, all the rules of logic require a 
continual diminution, and at last a total extinction 
of belief and evidence." But Hume clearly perceived 
that the human mind did not always function in con- 
formity with the laws of logic. Then followed natur- 
ally his psychological account of mathematics, — or 
rather, it may be said, of knowledge in general. 

III. The Psychological Treatment of Mathematics. 
— The psychological element is a most important fac- 
tor in Hume's theory of knowledge. It is the great 
head stone of the corner. It is not only an original, 
but a distinctively Anglo-Saxon contribution to phi- 
losophy. Pfleiderer has well said that "imagination 
and association are two genuine English powers, 
through which this people, on the ideal ground of 
poetry and in the magnificent arena of achievement, 
have brilliantly paid their tribute to the world's his- 
tory." Another tribute has similarly been paid in 
the subtle realm of speculative thought. 

After stating that the logical result of his episte- 
mological account of knowledge is a total extinction 
of belief and evidence, Hume proceeds:^ "Should it 
here be asked me, whether I sincerely assent to this 
argument, which I seem to take such pains to incul- 

1 Pp. 474, 475. « P. 474. 



124 Hume's treatise and inquiry. 

cate, and whether I be really one of those skeptics, 
who hold that all is uncertain, and that our judgment 
is not in any thing possessed of any measure of truth 
and falsehood; I should reply, that this question is 
entirely superfluous, and that neither I, nor any other 
person was ever sincerely and constantly of that opin- 
ion. Nature, by an absolute and uncontrollable neces- 
sity has determined us to judge as well as to breathe 
and feel. ' ' This determination of nature arises from 
custom or habit. Prom custom arises belief. And 
belief alone preserves the mind from total skepticism.^ 
But all demonstrative knowledge— arithmetic and al- 
gebra as well as geometry— is reduced to a species of 
probability. In short, the greatest degree of certainty, 
whether intuitive or demonstrative, is belief. ''Belief 
is more properly an act of the sensitive, than of the 
cogitative part of our natures,"^ and the degree of 
conviction attending it — although at times the con- 
viction is delusive^— "is sufficient for our purpose, 
either in philosophy or common life."* 

IV. Conclusion.— The answers of the Treatise to 
the first three questions that demand settlement have 
now been indicated. The answer to the first, is an 
unqualified negative. Mathematics is not an a priori 
science, but empirical, because its first principles are 
sensible. The answer to the second question is a 
qualified negative. Is mathematics an absolutely cer- 
tain science? It depends upon the meaning attrib- 
uted to absolute. Mathematics is not an absolutely 
certain science, in the sense of being a priori certain. 
For the human mind is finite; knowledge is relative; 
and in nearly all thinking processes there is a possi- 

1 P. 475. 2 ma, 3 cf. pp. 545, 547. * P. 476. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 125 

bility of error. But arithmetic and algebra are em- 
pirically certain. Geometry, of course, is not. In 
certain passages, however, it is said that arithmetic 
and algebra are perfectly exact and certain sciences.* 
Yes, those statements are in the epistemological ac- 
count, and are to be understood, therefore, in a pro- 
visional or relative sense. In the psychological ac- 
count, Hume holds that these sciences are practically, 
or empirically certain, not absolutely or a priori cer- 
tain. The answer to the third question is a divided 
one. Arithmetic and algebra are perfectly exact sci- 
ences; on the other hand, geometry is not. 

§ 23. Treatment of Mathematics in the Appendix. 
— In the appendix Hume added a few remarks on 
geometry, for the purpose of further explaining his 
meaning. These passages do not indicate any change 
of view from that expressed in the Treatise, and con- 
sequently, do not require extended comment. There 
is but one statement that seems to call for a word of 
explanation. ''If [mathematicians] employ," says 
the author,^ *'as is usual, the inaccurate standard, 
derived from a comparison of objects, upon their gen- 
eral appearance, corrected by measuring and juxta- 
position; their first principles, though certain and 
infallible, are too coarse to afford any such subtile 
inferences as they commonly draw from them. ' ' Here 
he speaks of the first principles of geometry as being 
"certain and infallible," whereas, in the Treatise he 
had regarded them as being inexact, and not precisely 
true.^ The inconsistency is only verbal. In the ap- 
pendix he does not mean, literally, that the first prin- 

' P. 374. 2 p. 357. 

3 Cf. pp. 350, 356, 373, 374. 



126 Hume's treatise and inquiry. 

eiples of geometry are ''certain and infallible," for 
he not only says that they are "too coarse" to afford 
such "subtile inferences" as are commonly drawn 
from them, but he immediately adds that they "are 
founded on the imagination and senses." And in 
another passage he asserts^ "that the only useful no- 
tion of equality, or inequality, is derived from the 
whole united appearance and the comparison of par- 
ticular objects." 

§ 24. Treatment of Mathematics in the Inquiry.— 
In the Inquiry, on the subject of mathematics, there 
is at once observable a great difference in the form 
of statement. Since Hume omits that portion of the 
Treatise which deals with space and time^ and conse- 
quently neglects to give a derivation of space, as he 
did formerly to give a derivation of number, the sci- 
ences of arithmetic, algebra, and geometry seem to 
stand upon the same basis of exactness and certainty ; 
and since he omits the account of philosophical rela- 
tions, the former distinctions between the different 
degrees of evidence not only fall into the background, 
but almost entirely disappear. The obvious result is 
that the author appears to have approached, if not to 
have adopted, the common sense view of mathematics.^ 
He divides "all the objects of human reason or in- 
quiry" into relations of ideas and matters of fact; 
and under relations of ideas he includes the sciences 
of arithmetic, algebra, and geometry, "and in short, 
every affirmation, which is either intuitively or demon- 
stratively certain."^ The propositions of mathe- 

iP. 352. 

2 Cf. pp. 107, 108, above. 

»P. 20; cf. p. 22, 135. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 127 

matics, he holds, * ' are discoverable by the mere opera- 
tion of thought, without dependence upon what is any- 
where existent in the universe. Though there never 
were a circle or triangle in nature, the truths, demon- 
strated by Euclid, would for ever retain their cer- 
tainty and evidence."^ 

The foregoing statement summarizes Hume's treat- 
ment of mathematics in the Inquiry. It corresponds 
to the epistemological account in the Treatise. Both 
the logical and psychological accounts are omitted in 
the later work. Naturally, therefore, it has been al- 
most universally supposed that there is a fundamental 
difference between the doctrine of mathematics in the 
Inquiry and that in the Treatise. The supposition, 
however, is without foundation. Had the logical and 
psychological accounts not been omitted, it is prac- 
tically certain that the position of both works, on this 
question, would have been identical. But why are 
these accounts omitted ? it may be asked ; does not this 
fact in itself indicate a change of view? Not neces- 
sarily, for Hume was here giving a popular exposition 
of the more easy and interesting parts of his system, 
and he reserved mathematics for special treatment 
on another occasion. Later, he wrote an essay on 
"The Metaphysical Principles of Geometry," but did 
not publish it, because Lord Stanhope convinced him 
that "either there was some defect in the argTiment, 
or in its perspicuity. ' '^ Even in default of this essay, 
there are several incidental references in the Inquiry 
which go far to prove that his view of mathematics is 
still essentially the same as that presented in the 
Treatise. 

1 P. 22; cf. pp. 10 n., 28, 37, 50, 51, 134. 

2 Cf. pp. 96, 97, above. 



128 hume's treatise and inquiry. 

Arithmetic, algebra, and geometry are not a priori 
sciences, but empirical. For Hume, in accordance 
with his principle that all ideas are copies of impres- 
sions, states explicitly that "the ideas of the mathe- 
matical sciences, being sensible, ' ' are always clear and 
determinate.^ ' ' All the ideas of quantity, ' ' he thinks,^ 
''upon which mathematicians reason, are nothing but 
particular, and such as are suggested by the senses 
and imagination." Since, therefore, the mathemat- 
ical sciences are empirical, they are not absolutely or 
a priori certain. "One may safely, . . . affirm," 
says Hume,^ "that if we consider [the moral and 
mathematical sciences] in a perfect light, their ad- 
vantages and disadvantages nearly compensate each 
other, and reduce both of them to a state of equality. ' ' 
The general view just indicated will be confirmed by 
a special consideration of geometry,— that branch of 
mathematics being treated somewhat more fully than 
is arithmetic or algebra. 

It has already been shown* that although Hume, 
in the Inquiry, omitted the treatment of space and 
time, yet his doctrine of space and time is similar in 
both works. It is not surprising, therefore, that he 
looks upon geometry as an empirical science. His 
position, as stated in section iv, corresponds with that 
of Hobbes. His meaning is, that "the truths" dem- 
onstrated by Euclid "for ever retain their certainty 
and evidence," after knowledge of the geometrical 
figures has once been acquired. Since, however, all 
geometrical figures are sensible, a knowledge of them 
is derived only through sense experience. In short, 
geometry in an inductive science. But it differs from 

iP. 50. 2 P. 129 n. 3 p. 50. *Pp. 95-97. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 129 

other inductive sciences in the fact that one instance 
serves as a sufficient basis for a generalization. ' ' The 
conclusions;, which [reason] draws from considering 
one circle, are the same which it would form upon 
surveying all the circles in the universe."^ Kant, it 
is true, mistakenly supposed Hume to regard geom- 
etry—or rather mathematics— as an analytical science. 
For this opinion, indeed, Hume gave some ground 
when he affirmed that the equality of the square on 
the hypothenuse of a right angled triangle to the 
squares on the two sides was a relation, '"discoverable 
by the mere operation of thought. ' ' But he explained 
his meaning when he declared that this relation could 
not "be known, let the terms be ever so exactly de- 
fined, without a train of reasoning and inquiry."^ 

Not only is geometry, as treated in the later work, 
an empirical science, but it is not a perfectly exact 
science. In the editions of 1748 and 1751, in a note 
appended to the twelfth section, Hume asserts:^ "In 
general, we may pronounce, that the ideas of greater, 
less, or equal, which are the chief objects of geometry, 
are far from being so exact or determinate as to be the 
foundation of such extraordinary inferences [as those 
arising from the doctrine of the infinite divisibility of 
space]. Ask a mathematician what he means, v/lien 
he pronounces two quantities to be equal, and he must 
say, that the idea of equality is one of those, which 
cannot be defined, and that it is sufficient to place two 
equal qualities before any one, in order to suggest it. 
Now this is an appeal to the general appearances of 
objects to the imagination or senses, and consequently 

1 P. 37 ; cf. Brede, Der Vnterschied d. Lehren H., p. 35. 

2 P. 134. 3 P. 129 11. 



130 Hume's treatise and inquiry. 

can never afford conclusions so directly contrary to 
these faculties. ' ' This passage was omitted after the 
edition of 1751, but the remainder of the note was 
retained. It contains the following sentences: *'If 
this be admitted [that there is no such thing as ab- 
stract or general ideas] (as seems reasonable) it fol- 
lows that all the ideas of quantity, upon which mathe- 
maticians reason, are nothing but particular, and such 
as are suggested by the senses and imagination, and 
consequently cannot be infinitely divisible. It is suffi- 
cient to have dropped this hint at present, without 
prosecuting it any farther." Now if all the ideas of 
quantity are "nothing but particular, and such as are 
suggested by the senses and imagination, " it is evident 
that geometry is not a perfectly exact science. That 
it contains "contradictions and absurdities," Hume 
explicitly affirms, if it be assumed that there are gen- 
eral ideas. He denies the assumption, however, and 
in that manner thinks to escape the contradictions. 
Yet his attempt to do this in the essay on ' ' The Meta- 
physical Principles of Geometry" does not appear to 
have been successful. 

Finally, it must be observed, that although Hume, 
in the Inquiry, omitted a specific criticism of reason 
and the senses, he said enough to indicate that the 
logical treatment of mathematics was omitted in the 
later work, not because he had changed his opinions 
on this subject, but because no "durable good or 
benefit to society" could be expected to result from 
such criticism.^ Thus he asserts :^ ' ' The chief objec- 
tion against all abstract reasonings is derived from the 
ideas of space and time ; ideas, which, in common life 

iP. 131. iPp. 128, 129. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 131 

and to a careless view, are very clear and intelligible, 
but when they pass through the scrutiny of the pro- 
found sciences . . . afford principles, which seem 
full of obscurity and contradiction. . . . The demon- 
stration of these principles seems as unexceptionable 
as that which proves the three angles of a triangle to 
be equal to two right ones, though the latter opinion 
be natural and easy, and the former big with contra- 
diction and absurdity. Reason here seems to be 
thrown into a kind of amazement and suspense^, . . . 
She sees a full light, which illuminates certain places ; 
but that light borders upon the most profound dark- 
ness. And between these she is so dazzled and con- 
founded, that she scarcely can pronounce with cer- 
tainty and assurance concerning any one object." 
Even with regard to ''the skeptical objections" to the 
reasonings concerning matters of fact, the author de- 
clares that, "while the skeptic insists upon these 
topics, he shows his force, or rather, indeed, his own 
and our weakness ; and seems, for the time at least, to 
destroy all assurance and conviction."^ But of 
course, as before, nature comes to the assistance of 
reason. The great subverter of ''excessive skepti- 
cism" is action. Nature is always too strong for prin- 
ciple.^ An evident implication of these passages is 
that although the mathematical sciences possess em- 
pirical certainty, no science possesses absolute or a 
priori certainty. 

It is now manifest that Hume's view of mathe- 
matics, in the Inquiry, is substantially the same as 
that in the Treatise. Arithmetic, algebra, and geom- 
etry are not a priori sciences, but empirical; for "the 

' P. 131. 2 lud. 



132 Hume's treatise and inquiry. 

ideas" of ''the mathematical sciences," having been 
derived from impressions, are "sensible."^ Arith- 
metic, algebra, and geometry are not absolutely or 
a 'priori certain sciences, for the advantages and 
disadvantages of the mathematical and moral sciences 
''nearly compensate each other, and reduce both of 
them to a state of equality."^ And geometry is not 
a perfectly exact science, for "all the ideas of quan- 
tity, . . . are nothing but particular, and such as 
are suggested by the senses and imagination."^ But 
Hume says that arithmetic, algebra, and geometry are 
"intuitively or demonstratively certain."* Very 
true; this is in his epistemological account. He 
made the same statement in the Treatise. He does 
not mean, of course, that the mathematical sciences 
are a 'priori intuitively or demonstratively certain. 
But he asserts that propositions in mathematics "are 
discoverable by the mere operation of thought."" 
Yes, he means after the ideas have been derived from 
sensible objects. Yet he also affirms, that "the only 
objects of the abstract sciences or of demonstration 
are quantity and number";*' that these sciences are a 
"more perfect species of knowledge "'^ than are mat- 
ters of fact; and that they are "the only proper ob- 
jects of knowledge and demonstration."^ In all these 
statements Hume, from his point of view, is perfectly 
correct. It is the traditional philosopher who is in 
error in inferring from them a priori exactness and 
certainty, through reading the thoughts of rationalism 
into the words of Hume. 

§25. References to Mathematics in Hume's other 



iP. 50. 


» lUd. 


3 P. 129 n. 


* P. 20. 


6 P. 21. 


6 P. 133. 


T lUd. 


8 P. 134. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 133 

Philosophical Works.— It avails little to appeal to 
Hume's other philosophical writings for additional 
information on this subject. Yet if such reference 
be made, it tends, on the whole, to confirm the con- 
clusion that has already been arrived at. In the 
Treatise of the Passions the author states:^ "The con- 
clusions [concerning the relations of ideas] are equally 
just, when we discover the equality of two bodies by 
a pair of compasses, as when we learn it by a mathe- 
matical demonstration ; and though in the one case the 
proofs be demonstrative, and in the other only sensi- 
ble, yet generally speaking, the mind acquiesces with 
equal assurance in the one as in the other." In the 
Treatise of Morals,'^ "If you assert, that vice and vir- 
tue consist in relations susceptible of certainty and 
demonstration, you must confine yourself to those four 
relations, which alone admit of that degree of evi- 
dence." In the Inquiry concerning the Principles of 
Morals,^ "It would be absurd ... to infer, that the 
perception of beauty, like that of truth in general 
problems, consists wholly in the perception of relations, 
and was performed entirely by the understanding or 
intellectual faculties." In the Dialogues concerning 
Natural Eeligion,^ "Let the errors and deceits of our 
very senses be set before us; the insuperable difficul- 
ties, which attend first principles in all systems; the 
contradictions, which adhere to the very ideas of mat- 
ter, cause and effect, extension, space, time, motion; 
and in a word, quantity of all kinds, the object of the 
only science, that can fairly pretend to any certainty 
or evidence. ' ' In short, the statements in the treatise 
on The Passions and in the Dialogues imply that the 
1 II, p. 223. 2 11, p. 240. » IV, p. 263. * II, p. 381. 



134 Hume's treatise and inquiry. 

mathematical sciences are empirical, and that geom- 
etry is not exact ; but those in the treatises on Morals 
do not seem to have exactly the same implication, al- 
though they have not necessarily a contrary one. 

The difference just noticed between the statements 
on mathematics in the treatise of The Passions and 
the Dialogues, and in the treatises on Morals is easily 
explained. Not only was Hume exceedingly indefi- 
nite in his use of terms, but he did not recognize the 
same criterion of truth when discussing theoretical 
subjects, as when discussing practical subjects. Re- 
plying to Elliot,— who held that ''an instinctive feel- 
ing" in the intellectual part of one's nature, "re- 
sembling the moral instinct in the moral part," 
corrects over refinement of subtlety or speculation,— 
he wrote :^ "Your notion of correcting subtlety of 
sentiment, is certainly very just with regard to morals, 
which depend upon sentiment; and in politics and 
natural philosophy, whatever conclusion is contrary 
to certain matters of fact, must certainly be wrong, 
and there must some error lie somewhere in the argu- 
ment, whether we be able to show it or not. But in 
metaphysics or theology, I cannot see how either of 
these plain and obvious standards of truth can have 
place. Nothing there can correct bad reasoning but 
good reasoning. And sophistry must be opposed by 
syllogisms. ' ' 

§ 26. Conclusion.— The results of the discussion 
may be summarized as follows:— 

1. The Faculties of Mind.— The more important 
mental faculties recognized by Hume are sensation, 
memory, imagination, reason, reflection, and instinct. 

1 Burton, Life, I, p. 324. 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 135 

He did not systematically classify, nor accurately de- 
fine them. He often experienced difficulty in de- 
scribing what he had in mind, and used, in both works, 
not only a variety of terms, but also, at different times, 
different terms to express the same thing. Most no- 
tably is this the case with regard to imagination and 
instinct. Knowledge begins with sensation. Mem- 
ory, imagination, and reason represent different stages 
of the same process. Reflection is a peculiar mixture 
of thinking and feeling. Instinct is not definable. It 
is often identified with imagination, habit, custom, or 
nature, and includes all those processes that cannot 
otherwise be explained. 

The only significant change, in the Inquiry, occurs 
in the treatment of instinct. Here Hume takes a 
place among modern psychologists. Instinct, having 
encroached on the domains of imagination, habit, and 
custom, becomes the faculty, par excellence. It mani- 
fests itself, at least by implication, below the level of 
consciousness, as tendencies to react upon the environ- 
ment. It subsists side by side with sensation, mem- 
ory, imagination, and reason, as impulses to action, 
and it appears at the higher end of consciousness, 
transcending reason, as the ultimate ends of action, 
ends for which reason can assign no reason.^ In this 
last sense, instincts— according to Hume,— or ideals of 
reason— according to the rationalistic philosophers,— 
are the assertion of the whole mind, the expression of 
the entire life of the individual. As such, they vary 
according to the stage of development of the person, 
of the community, of the nation, of the race. As 
people advance in civilization, contradictions natu- 
1 Cf. Everett, Essmjs: Theological and Literary, clis. I, VII. 



136 Hume's teeatise and inquiry. 

rally and necessarily arise between imagination and 
reason, and between reason and instinct. Hume saw 
clearly that, in a, world of progress^ the solution of all 
the contradictions of human experience is absolutely 
impossible. And he does not seem to have been far 
from the right track when he regarded the solution of 
these contradictions, so far as that is possible, to lie 
largely within the functions of imagination and in- 
stinct. In the treatment of his problem, however, he 
soon encountered insuperable difficulties, because biol- 
ogy, which opens the ante-room of psychology, was 
unable to lift the latch, being only in its infancy in 
his day. 

2. Intuitive Knowledge.— In the Treatise, intuitive, 
or sense and memory Imowledge is based on the philo- 
sophical relations of resemblance, contrariety, and 
degrees of quality, and arises immediately from the 
observation, or comparison of impressions and ideas. 
It is not necessarily exact, nor certain, but is condi- 
tioned by the nature of the object observed, and the 
capacity of the mind observing. In the Inquiry, the 
classification of philosophical relations is omitted, and 
naturally also a treatment of intuitive knowledge ; yet 
on this latter question, Hume's view, by implication, 
seems to be the same as f ornaerly. 

3. Demonstrative Knowledge.— Mathematics, or 
knowledge developed by reason, is based on the philo- 
sophical relation of proportions in number and quan- 
tity. In the Treatise, Hume gave three different, 
although not distinct or separate expositions of mathe- 
matics: an epistemological account in Parts II and 
III, a logical, and a psychological account in Part IV. 
According to the epistemological account, mathematics 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 137 

is an empirical science, because the ideas of number 
and quantity are derived from the senses; aritlunetic 
and algebra are perfectly exact and certain sciences, 
because they possess a ' ' precise standard ' ' ; but geom- 
etry is not an exact or certain science, because its first 
principles are based upon the general appearances of 
objects to the senses and imagination. According to 
the logical account, "all knowledge degenerates into 
probability," and would at last, were it not for the 
influence of custom, result in "a total extinction of 
belief and evidence. ' ' The psychological account pro- 
fesses to show how judgments in the mathematical 
sciences, like those in any other science, retain a cer- 
tain amount of assurance. Custom, or imagination, 
or instinct, or nature determines one by "an absolute 
and uncontrollable necessity ' ' to judge and to believe, 
as well as to breathe and feel. The degree of belief 
attending the judgment is, of course, greater in short 
and simple problems than in long and intricate ones. 
But in all cases, the quality or character of belief is 
the same, belief being "more properly an act of the 
sensitive, than of the cogitative part of our natures." 
In the Inquiry the logical and psychological ac- 
counts of mathematics are omitted. Hence, it has 
been the common opinion that Hume, in the later 
work, regarded mathematics as an absolutely certain 
science, based on a priori principles. And since, in 
the brief epistemological account that is given, arith- 
metic, algebra, and geometry seem to stand on an 
equal footing, the rationalistic philosophers, in ac- 
cordance with their favorite presuppositions, natu- 
rally thought that Hume had elevated geometry to 
the rank of an exact science. On the contrary, how- 



138 Hume's treatise and inquiry. 

ever, the facts of the matter are, that he first regarded 
arithmetic and algebra as being on an empirical basis 
equally with geometry, and later modified his episte- 
mological account to such an extent as to show that 
mathematics is not an absolutely certain science, and 
that geometry is not a perfectly exact one. 

The four questions proposed at the beginning of 
the discussion are now answered. (1) According to 
Hume, mathematics is not an a priori science; (2) it 
is not an absolutely certain science; (3) geometry is 
not a perfectly exact science; and (4) this seems to 
be the position of both the Treatise and Inquiry. It 
only remains yet to add a remark explanatory of the 
fourth answer, for as here stated, it is liable to mis- 
conception. Although it is true that, in neither worjk, 
is mathematics an a priori, or an absolutely certain 
science, nor is geometry a perfectly exact one ; it does 
not follow, by any means, that the general positions 
of the two works, on this subject, are identical. Log- 
ically, they are ; actually, they are not. Although the 
doctrine is essentially the same in the Inquiry as in 
the Treatise, the statement of it, as has repeatedly 
been pointed out, is quite different. And in this case, 
the difference in statement is so great that, without 
implying any change of view on the part of the author, 
it produces a very remarkable change in the tone and 
attitude of the book. While the doctrine of the 
Treatise is stated fully and boldly, that of the Inquiry 
is expressed briefly and hesitatingly. Yet the differ- 
ences in the later work are only of such a nature as 
can easily be explained. They arise from the omis- 
sion of the logical and psychological accounts of 
mathematics. And these omissions were made be- 



KNOWLEDGE, INTUITIVE AND DEMONSTRATIVE. 139 

cause: (1) Hume aimed, in the Inquiry, to give a 
brief and popular exposition of his theory of knowl- 
edge; (2) he intended to deal with mathematics at 
some future time; and (3) he thought that no "dur- 
able good or benefit to society" could be expected to 
result from a detailed statement of the skeptical ob- 
jections against reason or the senses. 

When Hume maintains that mathematics is an em- 
pirical science, and consequently, not possessed of 
absolute or a priori certainty, he is indubitably right. 
But when, through his failure to perceive that the 
fundamental characteristic of general ideas is the 
epistemological element, he contends that geometry is 
not a perfectly exact science, he is unquestionably 
wrong. As Aristotle held that, in any science, one 
should expect only that degree of accuracy which is 
conformable to the nature of the subject; so Hume 
held that the different sciences, being all empirical, 
admit of varying degrees of exactness and certainty, 
according to the nature of the subject-matter. But 
Hume, again like Aristotle, did not succeed, in all 
respects, in carrying out his principle. The limita- 
tions of his time, and his own psychical predisposition 
— his visualizing imagination,— were obstacles too 
great for his philosophical genius entirely to overcome. 



CHAPTER VII. 

THE IDEA OF CAUSE AND EFFECT. 

§ 27. Causation the Basis of Reasoning Concern- 
ing Matters of Fact.—Th.Q idea of causation has been 
an object of reflection ever since the dawn of rational 
speculation, and the validity of belief in causality has 
frequently been questioned throughout the history of 
philosophical inquiry. Egyptian and Jewish, Hindoo 
and Persian, Greek and Roman,— all historical races 
have had their distinctive representatives of empiri- 
cism and skepticism. It is in English philosophy, 
however, by intensely practical men, that the idea of 
cause and effect has been subjected to the most search- 
ing examination. Glanvill affirmed emphatically, that 
necessary connection is not perceivable by the senses. 
Hobbes, Locke, and Berkeley followed, more or less 
closely, along the same line of Pyrrhonism. They 
prepared the way for Hume. And although Hume, 
in his criticism of the idea of cause and effect, did 
little more, perhaps, than sum up and present in a 
new form the logical results of his predecessors' re- 
flection; nevertheless, to him belongs the distinctive 
honor of being the first philosophical writer, who gave 
a final analysis of the conception of causality from 
the standpoint of pure empiricism. Hume's exam- 
ination of the idea of cause and effect is not only an 
invaluable contribution to speculative thought, but 
also an imperishable monument to the intellectual 
acumen and subtle analytical power of one of the 
greatest of the many keen thinkers of Scotland. 

140 



THE IDEA OP CAUSE AND EFFECT. 141 

Cause and substance are the two poles of the phi- 
losophy of human nature. Having treated intuitive 
knowledge and demonstrative, Hume proceeded to 
deal with that division of probability which he calls 
proofs, reasoning proper, moral, or experiential. 
This species of reasoning is conversant with matters 
of fact. It is not, like intuitive and demonstrative 
knowledge, founded on the relations of resemblance, 
contrariety, degrees of quality, and proportions in 
number or quantity ; for since the contrary of matters 
of fact is conceivable, and therefore possible, knowl- 
edge of them is not obtained by means of reason. 
Nevertheless, the "arguments" in experiential, or 
empirical reasoning are regarded as being ''entirely 
free from doubt and uncertainty."^ 

All reasoning is of the nature of comparison. In 
comparison, one of the two objects compared, or 
neither, or both may be present to the senses or 
memory.2 If neither object is present, the reasoning 
is purely hypothetical.^ This statement is analogous 
to Kant's famous dictum, "concepts without percepts 
are empty." When the two objects are present to 
the senses or memory, the act is called "perception 
rather than reasoning." Similarly Kant said that 
"percepts without concepts are blind." When the 
two objects are present to sense or memory, the com- 
parison is based on the relations of identity and con- 
tiguity.* But in instances of comparison when only 
one object is present to the senses or memory, there 
is a conclusion drawn beyond experience. This is 
reasoning proper, or experiential reasoning. Its basis 

II, p. 423. 2 1, pp. 376, 384, 385; IV, p. 39. 

3 1, pp. 384, 385, 390; IV, p. 39. <I, p. 376. 



142 Hume's treatise and inquiry. 

is the relation of cause and effect.^ In order, there- 
fore, to discover the evidence for reasoning concern- 
ing matters of fact; that is, to learn the rational 
ground of experiential reasoning, it is necessary to 
examine the idea of cause and effect.^ 

§ 28. Examination of the Idea of Cause and Effect. 
—The treatment of causation, in the two works, al- 
though similar in form, differs much in detail. In 
the Treatise, the discussion is exceedingly thorough, 
systematic, and ingenious. In the Inquiry, on the 
other hand, it is brief and comparatively simple;— 
chiefly, no doubt, because Hume was afraid that 
should he ''multiply words about it, or throw it into 
a greater variety of lights, it would only become more 
obscure and intricate."^ Pfleiderer* states that the 
argument in the Treatise, like that on causation in 
Kant 's Kritik, proceeds analytically, while the reason- 
ing in the Inquiry, as in the Prolegomena, proceeds 
synthetically. Rather it should be said, that the 
argument in both cases is essentially analytical, but 
in the later work the analysis is less prominent than 
in the earlier. 

In accordance with his usual method of argumenta- 
tion, Hume, in both works, opens the discussion by 
inquiring after the origin of the idea.^ On this line 
of attack upon rationalism he had often won, and he 
again feels confident of achieving his wonted success. 
In the Inquiry, he states briefly, and then proceeds 
to prove, that the knowledge of the relation of cause 
and effect is not attained by intuitive perception, nor 

II, p. 376; IV, p. 24. 2 i, p. 377; IV, p. 24. 3 p. 63. 
*Einpirismus u. 8kepsis, p. 169 and n. 
51, p. 377; IV, p. 24. 



THE IDEA OP CAUSE AND EFFECT. 143 

by a priori reasoning, "but arises entirely from ex- 
perience."^ In the Treatise, Hume is at his best in 
the discussion of causation. Slowly and thoroughly 
he prepares for an exhaustive analysis of his problem, 
and then, with rare skill and subtle penetration, he 
winds his tortuous way through an argument of 
nearly one hundred pages, until finally he reaches his 
intended goal. It may be thought that the idea of 
cause and effect is derived by means of the senses, or 
by means of reason, or by means of a supra-natural 
power, or by means of the imagination. These are 
the only possible sources; and Hume examines them 
all. He first asserts that the impression of causation 
is not perceived as a quality of objects ; consequently, 
the idea "must be derived from some relation among 
objects."- Next he inquires what relations are dis- 
coverable between objects that are "considered as 
causes or effects." These are two: (1) contiguity, 
(2) succession.^ It is supposed, however, that there 
is still another element in causation, viz., necessary 
connection; that is, that there is a necessary connec- 
tion between objects or events that are causally re- 
lated. Moreover, it is the element of necessary con- 
nection which is always regarded as the essential part 
of causality. Hence this is the peculiar problem to 
be investigated.^ But necessary connection among 
objects or events is not perceived by the senses either 
as a quality, or as a relation. Then Hume deems it 
advisable "to leave the direct survey" of the ques- 
tion, and "beat about all the neighboring fields." In 
this manner he hopes to find "a hint" that may serve 
to clear up the difficulty.* He soon discovers a clue 

» Pp. 24, 25. «P. 377. 'Pp. 377, 378. <P. 379. sP. 380. 



144 Hume's treatise and inquiry. 

in two questions bearing on the subject, one the gen- 
eral question of causation, the other the particular 
question. These two questions he then examines in 
succession ; whereupon, he conies back to the point at 
which he turned aside, and deals directly with the 
idea of necessary connection. Accordingly, the treat- 
ment of the relation of cause and effect falls into 
three main divisions:— 

I. The general question of causation.* 
II. The particular question of causation.'' 

III. The idea of necessary connection.' 
The accounts in both works may be examined to- 
gether. 

I. The general Question of Causation. The gen- 
eral question of causation is stated in the Treatise as 
follows:* "For what reason we pronounce it neces- 
sary, that every thing whose existence has a begin- 
ning, should also have a cause ? ' ' and in the Inquiry : ' 
"What is the foundation of all our reasonings and 
conclusions concerning [the relation of cause and 
effect]?" These two questions, though differently 
expressed, are essentially the same. Huxley® asserts 
that the evidence by which Hume supports his con- 
clusion in the Inquiry, concerning the general ques- 
tion of causation, "is not strictly relevant to the 
issue." And several writers' state that he omits al- 

1 I, pp. 380-383 ; IV, pp. 24-38. 

2 I, pp. 383-422; IV, 24-47. 

3 I, pp. 450-466; IV, pp. 50-65. 

*P. 380. 5 p. 28. 6 Hume, p. 118. 

' Cf. Selby-Bigge, Hume's Enquiries, Introd. ; Ueberweg- 
Heinze, Oesch. d. Phil., Ill, p. 201 ; Eielil, Der philosopMsche 
Kriticismus, I, p. 114 and n.; Vaihinger, Eommentar ssu 
Kant's Kritik, 1, pp. 347, 349. 



THE IDEA OF CAUSE AND EFFECT. 145 

together the consideration of this question in the later 
work. Now it may be admitted that part, at least, 
of the evidence by which he supports his conclusion 
in the Inquiry is not strictly relevant. But it is 
contended that the two questions, as above stated, 
are for Hume's purposes practically equivalent.^ 
They imply each other in such a manner that the 
answer to both is the same. 

In the Treatise, the author professes to show that 
neither intuition, nor demonstration,— neither the 
senses and memory, nor thought and reasoning— is 
the ground of the opinion that every effect must have 
a cause. For if the necessity of a cause for every 
effect could be intuitively perceived, or could be 
demonstrated by reason, the contrary would be in- 
conceivable. But that the contrary is not inconceiv- 
able, he claims to prove by the following argument:'' 
"As all distinct ideas are separable from each other, 
and as the ideas of cause and effect are evidently dis- 
tinct, it will be easy for us to conceive any object to 
be non-existent this moment, and existent the next, 
without conjoining to it the distinct idea of a cause 
or productive principle. ' ' Accordingly, he concludes 
that the opinion of the necessity of a cause for every 
effect arises wholly from ''observation and experi- 
ence.'" In the Inquiry,* Hume asserts that "the 
knowledge" of the relation of cause and effect "is 
not, in any instance, attained by reasonings a priori," 
nor by the intuitive perception of the qualities of 
objects, "but arises entirely from experience." His 
chief argument is similar to that in the Treatise: 

Wf. Caird, The Critical Phil, of Kant, 1, p. 133 n.; Jahn, 
D. H. Causalitdtstheorie, pp. 6, 41. 

2P. 381. sp. 3&3. *P, 24. 

10 



146 Hume's treatise and inquiry. 

''Every effect is a distinct event fr.om its cause. "^ 
Consequently, it follows that ''there is not, in any 
single, particular instance of cause and effect, any 
thing which can suggest the idea of power or neces- 
sary connection. ' '^ Of course when one abandons the 
atomistic view of mind, the petitio principii in this 
reasoning becomes obvious. But on Hume's presup- 
positions the argument is perfectly valid. If "every 
effect is a distinct event from its cause," or if it is 
easy "to conceive any object to be non-existent this 
moment, and existent the next, without conjoining to 
it the distinct idea of a cause or productive principle, ' ' 
there is no real necessity to think that every effect 
must have a cause ; and the supposed necessity, so far 
as it exists, must be explained on the ground of ex- 
perience. 

The next question should naturally be, how experi- 
ence gives rise to the opinion, that "whatever begins 
to exist, must have a cause of existence?"^ But in 
the Treatise, Hume finds it "more convenient to sink 
this question ' ' in the particular problem of causation, 
remarking: "It will, perhaps, be found in the end, 
that the same answer will serve for both." And in 
the Inquiry, instead of asking how experience gives 
rise to the principle that every event must have a 
cause? he asks a related question, viz., "What is the 
foundation of all conclusions from experience?"* 
These two questions, that of the Treatise and that of 
the Inquiry, may now be considered. 

II. The particular Question of Causation. The 
particular question of causation resolves itself into 

1 P. 27. «P. 52. ap. 383. 4 p. 28. 



THE IDEA OF CAUSE AND EFFECT, 147 

three parts :^ (1) ''Why we conclude, that such par- 
ticular causes must necessarily have such particular 
effects?" (2) "What is the nature of that inference 
we draw from the one to the other?" (3) What is 
the nature of "the belief" we repose in the inferred 
idea ? The last of these problems will be left for con- 
sideration in the following chapter. The first ques- 
tion does not receive separate treatment, but is dealt 
with incidentally in connection with the second, Hume 
making the characteristic remark: "Perhaps it will 
appear in the end, that the necessary connection de- 
pends on the inference, instead of the inference de- 
pending on the necessary connection."' Consequently, 
the subject of immediate interest is the second division 
of the particular question of causation, viz., "Why 
we form an inference from one [instance] to an- 
other ? ' ' And this question, it may be noted, resolves 
itself into that of the Inquiry at present under in- 
vestigation; for the reason or ground on which we 
form an inference from one instance to another is, 
according to Hume, ' ' the foundation of all conclusions 
from experience." 

The argument may now be presented in two forms, 
as the mode of reasoning is not exactly the same in 
both works. This change of method, however, seems 
to have arisen from Hume's different ways of stating 
the problem, or perhaps from his desire for brevity 
of treatment in the Inquiry. In the Treatise,' the 
author gives a brief account of experience, professing 
to show how, from the observation of antecedent and 
consequent in a number of particular instances, the 
idea of cause and effect gradually arises. The infer- 

II, pp. 380, 383. 21, p. 389. sPp. 388, 389. 



148 humb's teeatise and inquiry. 

ence, therefore, from cause to effect, or from effect to 
cause is a transition of the mind from "a present 
impression of sense or memory" to a related idea. 
And the transition is founded, not on such a penetra- 
tion into the "essences" of objects "as may discover 
the dependence of the one upon the other," but on 
past experience. Then the question occurs, whether, 
the transition is produced by reason, or by imagina- 
tion ?^ Were it produced by reason, it would be based 
on the principle of the uniformity of nature. Hence 
the following question presents itself, what is the 
ground of the principle of the uniformity of nature? 
This principle is not established on intuitive knowl- 
edge, nor on demonstrative,— that is, it is not derived 
from the senses, nor from reason,— because a change 
in the course of nature is conceivable. Neither is it 
derived from probability, for probability is founded 
upon it. '^ Eather it arises from constant conjunction 
or custom, and is, therefore, an assumption that can 
never be proved.' Consequently, the transition or 
inference is not produced by reason, but by imagina- 
tion, by means of the two primary laws of association, 
resemblance and contiguity, that is, through the repe- 
tition of similar instances or custom.* 

According to the Inquiry, all conclusions from ex- 
perience "proceed upon the supposition, that the 
future will be conformable to the past."® But then 
it must be asked, as before, what is the ground of the 
principle of the uniformity of nature? This prin- 
ciple does not rest upon demonstrative arguments, 

iP. 390. 2P. 391. 3Pp. 392, 431, 545. 

*Cf. pp. 390, 393, 403, 414, 459, 461, 471, 509. 
sPp. 29, 31, 33. 



THE roEA OP CAUSE AND EFFECT. 149 

since a change in the course of natur.e implies no 
contradiction.^ Neither does it rest upon probable 
reasoning or argiunents from experience, since "all 
these arguments" are founded on the principle of 
the uniformity of nature.^ This principle is merely 
an assumption, a product of the imagination which 
arises from the constant conjunction of similar in- 
stances." Consequently, **the foundation of all con- 
clusions from experience ' ' is constant conjunction and 
custom.* Hence these two forms of the argument 
are ultimately one and the same. Constant or cus- 
tomary conjunction of resembling objects has such an 
influence upon the imagination, that on the appearance 
of one the mind passes on to the thought of the other ; 
or as otherwise put, resembling impressions and ideas 
that have been constantly conjoined introduce one 
another, so that the repetition of similar instances 
carries the mind beyond actual experience, and causes 
it to expect similar instances in the future under 
similar conditions. Inference, therefore, is not an 
act of intuition,— of sense perception,— nor a process 
of demonstration, but is a transition of the imagina- 
tion produced by custom. "The foundation of all 
conclusions from experience" also, is ultimately cus- 
tom or habit. The nature of custom, however, the 
author professes, in each work, not to explain. It is 
a species of instinct, or "a principle of human nature, 
which is universally aclmowledged, and which is well 
known by its effects."^ But as in the case of the 
principles of association of ideas, no explanation of 

1 Pp. 31, 33. 2 Ibid. 3 Pp. 30, 32, 33. * Pp. 36, 37, 39, 40. 
5 I, pp. 471, 475; IV, pp. 37, 40, 131. 



150 Hume's treatise and inquiry. 

it can be given, except that furnished by experience 
and analogy/ 

It is now manifest that, in his treatment of the par- 
ticular question of causation, Hume has answered — 
at least after his own fashion— the question in the 
Treatise for which the particular one was substituted, 
viz., how experience gives rise to the principle that 
"every thing whose existence has a beginning should 
also have a cause?" He had formerly shown that 
this principle is a conclusion from experience;^ now 
he has explained the nature of inference, or experi- 
ential reasoning ; therefore, he has shown, how experi- 
ence gives rise to the principle that every event must 
have a cause. ^ He has answered this question in 
the Inquiry also. In the Inquiry he asked, what is 
the foundation of all conclusions from experience? 
Therefore he asked, at least by implication, what is 
the foundation of the principle that every event must 
have a cause ?— that principle being a conclusion from 
experience. And to explain that "the foundation of 
all conclusions from experience" is constant conjunc- 
tion and custom, is equivalent to showing how experi- 
ence gives rise to the principle that every event must 
have a cause. This mode of handling the matter is 
certainly ingenious. Under the form of many ques- 
tions, Hume arranged the argument to suit his con- 
venience, and implicitly assumed one of the main 
points to be proved.* To this assumption, of course, 
he was fully entitled, according to the fundamental 
principles of his system of philosophy. And it may 

1(7/=. 1, pp. 321, 330, 392, 393, 471; IV, p. 37. 

2 Cf. p. 144, above. 3(7/. I, p. 389. 

*Cf. I, pp. 380, 381, 383, 385, 390; IV, pp. 24, 27, 30, 31. 



THE IDEA OF CAUSE AND EFFECT. 151 

be noted that, on discarding this assumption, viz., that 
all perceptions are distinct and separable, Hume's 
position, although bereft of one of its conspicuous 
supports, is, in its essential import, or with but slight 
modifications, perfectly valid. 

Logically, the next question for discussion is the 
third part of the particular question of causation, 
viz., the nature of belief. But as it seems advisable 
to devote a chapter to this topic, we pass on to the 
last general division, that is, necessary connection. 

III. The Idea of Necessary Connection. — In the 
fourteenth section of Part III of the Treatise, and in 
the seventh section of the Inquiry, Hume returns to 
the question which was left unanswered at the begin- 
ning of the discussion, and which was supposed to be 
conversant with the chief element of the idea of cause 
and effect, viz., the question of necessary connection.^ 
But having answered, in the manner that he did, the 
first two questions— the general one, and the particular 
one,— he has practically answered the third, that of 
necessary connection. For if nothing is known about 
causation except what is derived from experience, and 
if the ultimate ground of experience is custom, or 
instinct, then there is no element of necessity, as com- 
monly understood, in the idea of cause and effect. 
As Hume asserts :^ ' ' The necessary connection betwixt 
causes and effects is the foundation of our inference 
from one to the other. The foundation of our in- 
ference is the transition arising from the accustomed 
union. These are, therefore, the same." Thus he 
arrives by a process of reasoning at a conclusion sim- 
ilar to the assumption with which he had started out : 

1 I, p. 379. 2 I, p. 460. 



152 Hume's treatise and inquiry. 

"As all distinct ideas are separable from each other, 
and as the ideas of cause and effect are evidently dis- 
tinct, it will be easy for us to conceive any object to 
be non-existent this moment, and existent the next, 
without conjoining to it the distinct idea of a cause 
or productive principle."^ So far as we know, there- 
fore, or are capable of knowing, objects or events are 
related only by means of association and custom. 
Hence Hume, in explaining necessary connection, has 
really explained it away. Necessity exists only in 
the mind, not in objects. *' Either we have no idea 
of necessity," he says,^ "or necessity is nothing but 
that determination of the thought to pass from causes 
to effects, and from effects to causes, according to 
their experienced union. ' ' It might only remain now 
for Hume to show how the fiction of necessary con- 
nection has arisen. But as he has just examined ' ' one 
of the most sublime questions in philosophy," he 
thinks it may be advisable to give a fuller account of 
his doctrine. For that reason, he brings forward 
some additional arguments to show that the idea is 
invalid. The two topics will be treated separately. 
1. The idea of necessary connection is invalid. As 
usual, in testing the validity of any idea, Hume brings 
forward his "articles of inquisition," and demands 
from what impression the idea of necessary connec- 
tion is derived?^ It is not derived by means of the 
senses, from the observation of objects, because the 
only relations perceivable among objects are contiguity 
and succession.* It is not derived by means of thought 

1 I, p. 381; IV, p. 27. « I, p. 460; IV, p. 62. 

3 1, p. 450; IV, p. 52. ^ lUd. 



THE IDEA OF CAUSE AND EFFECT. 153 

or reasoning, because reason can produce no new idea. ^ 
And it is not derived from a ' ' supreme spirit ' ' or the 
operations of "deity," as the Cartesians held, for the 
doctrine of innate ideas has been rejected, and power 
is not discoverable in spirit any more than in body.'' 
These are the main arguments adduced, and thus far 
the reasoning, in both works, though different in form, 
is identical in import. 

In the Treatise, however, Hume incidentally ad- 
mitted that if the idea of power were once acquired, 
power might be attributed to " an unknown quality. ' ' * 
This admission seems to have been seized upon by his 
opponents as a point of vantage, for an additional 
argiunent was introduced in the appendix to refute 
those who assert "that we feel an energy, or power, 
in our own mind," and then "transfer that quality 
to matter. " " But to convince us how fallacious this 
reasoning is," says Hume,* "we need only consider, 
that the will being here considered as a cause, has no 
more a discoverable connection with its effects, than 
any material cause has with its proper effect. So far 
from perceiving the connection betwixt an act of 
volition, and a motion of the body ; it is allowed that 
no effect is more inexplicable than the powers and 
essences of thought and matter. Nor is the empire 
of the will over our mind more intelligible. ... In 
short, the actions of the mind are, in this respect, the 
same with those of matter. We perceive only their 
constant conjunction ; nor can we ever reason beyond 

1 I, p. 452; rV, pp. 52, 53. 

2 I, pp. 454, 455; IV, pp. 58, 59, 60. » I, p. 455. 

* I, p. 455; cf. p. 541 for a vei'bal contradiction of the last 
sentence. 



154 Hume's treatise and inquiry. 

it. No internal impression has an apparent energy, 
more than external objects have." This argument 
was again brought forward in the Inquiry, and pre- 
sented with considerable fulness .of detail,^ Its im- 
portance was probably overlooked, or underestimated 
in the earlier work. This is one of the very few 
instances in which there is any development in the 
Inquiry, of Hume's doctrine. Otherwise the argu- 
ment has little significance, for it had been implied 
in the Treatise.^ The conclusion of the reasoning in 
both books is exactly the same, viz., one never has an 
impression of power or necessary connection, and con- 
sequently cannot obtain a valid idea of it. 

2. How the Fiction of necessary connection arises. 
It is thought, however, that one has an idea of power, 
or of necessary connection between objects or events ; 
hence, the author's next task is to account for this 
fiction. Concerning the origin of the idea, the ex- 
planation of the two works is identical.^ It is briefly 
as follows: One event is observed to follow another 
immediately; when this instance of two events in 
immediate succession has been repeated a number of 
times, the repetition, through custom, or instinct, pro- 
duces a new sentiment or feeling, an impression of 
reflection; and this impression of reflection gives 
rise to the idea of power or necessary connection. 
"Necessity, then," says Hume,^ "is the effect of this 
observation, and is nothing but an internal impression 
of the mind, or a determination to carry our thoughts 
from one object to another." Thus the idea of power 
or necessary connection is a product of the imagina- 
tion. 

1 Pp. 54-57. 2 p. 455. 

3 I, pp. 457, 458; IV, pp. 61, 62. *I, p. 459; cf. IV, p. 63. 



THE IDEA OF CAUSE AND EFFECT. 155 

In the Treatise/ the author expressed an apprehen- 
sion that although his "foregoing reasoning" appeared 
to him "the shortest and most decisive imaginable," 
yet "with the generality of readers" the bias of the 
mind to regard necessary connection as something 
objective would prevail, and give them a prejudice 
against his doctrine. This bias he explained in the 
following manner:^ "It is a common observation, that 
the mind has a great propensity to spread itself on 
external objects, and to conjoin with them any internal 
impressions which they occasion, and which always 
make their appearance at the same time that these 
objects discover themselves to the senses. . . . The 
same propensity is the reason, why we suppose neces- 
sity and power to lie in the objects we consider, not 
in our mind, that considers them." These remarks 
are omitted in the Inquiry. But the omission is not 
significant, since the same explanation of the bias of 
mind here referred to is implied in a foot-note,' and 
is again stated in The Natural History of Beligion.* 

TV. Conclusion. Hume's account of necessary 
connection, particularly that in the Treatise, is by no 
means so simple as might appear from the above state- 
ment. The discussion abounds in repetitions, obscuri- 
ties, and even inconsistencies. Yet the inconsistencies 
are often verbal rather than real, arising from the use 
of terms, sometimes purposely, in a loose and popular 
sense. It is allowed, for instance, that there are 
powers and operations of nature;* also power or effi- 
cacy is spoken of as uniting causes and effects." But 
Hume explains that, "in all these expressions, so ap- 
plied, we have really no distinct meaning, and make 

1 P. 461. 2/&icZ. 3 P. 64. * IV, p. 317. sp. 462. 6 p. 450. 



156 Hume's teeatise and inquiry. 

use only of common words, without any clear and 
determinate ideas. "^ Again, the idea of power, of 
necessity, or of necessary connection is said to arise 
from a new impression, or determination,^ from sim- 
ilar instances, or the observation of similar instances, * 
from an internal impression, or impression of reflec- 
tion,^ from a propensity,-'' from the repetition of re- 
lated objects,* from habit or custom,'^ and from imag- 
ination.^ If Hume had enjoyed the opportunity of 
presenting his system of philosophy in the class room, 
or had experienced the necessity of defending it as he 
formulated it, he would have been more precise in his 
use of terms, and more consistent in his form of ex- 
pression. His various accounts of the derivation of 
the idea of necessary connection may be summarized 
briefly as follows: The terms efficacy, agency, power, 
force, energy, necessity, connection, and productive 
quality, "are all nearly synonymous."® Repetition,^" 
custom,^^ similar instances,^^ constant conjunction,^^- 
instinct,^* or imagination^^ produce a determination 
of the mind, a propensity, habit, customary transition, 
or impression of reflection. This determination,^'' pro- 
pensity,^'^ habit,^^ customary transition^"— qualities of 
perceptions,^" — or internal impression^^ is equivalent 
to power, necessity, or necessary connection. The idea 



iP. 457; cf. IV, p. 29 n, 




2 Pp. 450, 451, 463 




3 Pp. 457, 459. 




* P. 460. 


6 Ibid. 


6 P. 461. 




7 P. 508. 


^8 P. 511. 


SI, p. 451; IV, p. 51. 




101, pp. 450, 461. 




"Pp. 460, 464, 511. 




12 P. 459. 


lap. 464. 


up. 471. 




15 Pp. 464, 511. 




16 Pp. 451, 459, 460, 461, 


463. 




"P. 460. 


18 Pp. 429, 508. 




18 P. 461. 


20 Ibid. 


21 Pp. 459, 460. 









THE IDEA OF CAUSE AND EFFECT. 157 

of power, of necessity, or of necessary connection is a 
copy of an internal impression, or impression of reflec- 
tion. ^ Consequently, the idea of power, of necessity, 
or of necessary connection arises immediately or di- 
rectly from a determination of the mind, propensity, 
habit, customary transition, internal impression, or 
the imagination; and mediately or indirectly from 
repetition of related objects, observation of similar 
instances, constant conjunction, custom, or instinct. 

§ 29. Misconceptions of Hume's Critics.— 'From, the 
above examination of Hume's treatment of the idea 
of cause and effect, it is evident that the position of 
both works is substantially identical. " There are dif- 
ferences in the manner of statement, it is true, but 
these do not seem to be significant. Some of Hume 's 
interpreters, however, put forward the claim that, 
with respect to certain aspects of the question, there 
are real and important differences in the Inquiry. 
The opinions of these writers, as well as a few mis- 
conceptions of others regarding Hume's view of 
causality call for some further consideration. 

Selby-Bigge^ also asserts that, in the Inquiry, *'the 
tiguity practically drops out altogether" in ''the 
account of the origin, in particular cases, of the idea 
of cause and effect"; and that "the account of causa- 
tion, ... is left hanging in the air when the sup- 
port of the theory of succession has been withdrawn." 
There does not seem to be sufficient ground to warrant 
these statements. Hume, it is true, affirms that "all 

1 Pp. 454, 460, 463. 

2 Cf. Brede, Der Unterschied d. Lehrcn E., p. 39 ; Pfleiderer, 
Empirismus u. Skepsis, p. 169 and n, 

^ Hume's Enquiries, pp. xiii, xv. 



158 Hume's treatise and inquiry. 

arguments from experience are founded on the sim- 
ilarity, which we discover among natural objects, and 
by which we are induced to expect effects similar to 
those, which we have found to follow from such ob- 
jects.-'^ In like manner he had expressed himself in 
the Treatise.^ The passage just quoted, however, and 
several others in the Inquiry of a like import, do not 
mean that the relation of resemblance has now as- 
sumed the functions formerly exercised by contiguity 
and succession in explaining the origin, in particular 
cases, of the idea of cause and effect. On the con- 
trary, several statements clearly indicate that the 
relations of contiguity and succession play, respec- 
tively, the same role here as in the earlier work. 
Thus Hume asserts:^ "Suppose a person, though en- 
dowed with the strongest faculties of reason and re- 
flection, to be brought on a sudden into the world; 
he would, indeed, immediately observe a continual 
succession of objects, and one event following an- 
other; but he would not be able to discover anything 
farther. . . . Suppose again, that he has acquired 
more experience, and has lived so long in the world 
as to have observed similar objects or events to be 
constantly conjoined together; what is the conse- 
quence of this experience? He immediately infers 
the existence of one object from the appearance of 
the other." Also, when speaking of the idea of 
necessary connection, he says:* "All events seem 
entirely loose and separate. One event follows an- 
other ; but we never can observe any tie between them. 
They seem conjoined, but never connected." And in 

iP. 31. 2 p. 391. 

3 Pp. 36, 37; cf. pp. 24, 30, 33. * P. 61. 



THE IDEA OF CAUSE AND EFFECT. '159 

a note in the edition of 1751 he made the decisive 
remark:^ *'A cause is different from a sign; as it 
implies precedency and contiguity in time and place, 
as well as constant conjunction. ' ' The fact that con- 
tiguity is omitted in the definitions of cause given in 
the Inquiry is not significant, since the meaning of 
the word is clearly implied.^ 

Selby-Bigge^ also asserts that, in the Inquiry, "the 
distinction between causation as a philosophical and 
a natural relation is altogether dropped." This 
statement is not justified. In the Treatise,* Hume 
gave two definitions of cause, one as a philosophical 
relation, the other as a natural relation. In the In- 
quiry,^ he gave two corresponding definitions. These 
are briefer than those in the Treatise, but they are 
similar in meaning. For reasons already given,® the 
author omitted in the later work an explicit distinc- 
tion between natural and philosophical relations. As 
might be expected, therefore, in the definitions of 
cause, this distinction, although implied, is not form- 
ally expressed. In the section on "Liberty and 
Necessity," this same distinction is again implied. 
Hume asserts:'^ "Necessity may be defined two ways, 
conformably to the two definitions of cause, of which 
it makes an essential part. It consists either in the 
constant conjunction of like objects, or in the infer- 
ence of the understanding from one object to an- 
other." That is, necessity, like cause, may be re- 
garded either as a philosophical, or as a natural 

» IV, p. 64. 2 IV, p. 63; cf. p. 79. 

^ Hurne's Enquiries, Introd. <P. 465. 

5 P. 63 ; cf. Brede, Der Unterschied d. Lehren H., p. 39. 

6 Pp. 80-83. ^ P. 79. 



160 Hume's treatise and inquiry. 

relation. Selby-Bigge 's account of Hume's treat- 
ment of causation is somewhat obscure, no doubt 
owing to brevity of statement. Indeed it hardly 
appears to be perfectly consistent. For although he 
says that "contiguity practically drops out alto- 
gether" in the account of the origin, in particular 
cases, of the idea of cause and effect; he also says: 
"Contiguity, , . . drops out of the Enquiry as a 
philosophical relation, though it must be supposed to 
exert its influence as a natural relation. ' '^ It is suf- 
ficient to remark here that Selby-Bigge 's distinction 
between natural and philosophical relations does not 
exactly conform to that of Hume. Indeed the editor 
of Hume's Enquiries does not seem to be quite free 
from the bondage of that "relationism" which 
weighed like a nightmare on the mind of Green, and 
still vexes sore the souls of his readers. 

According to Peterson,^ the explanatory definition 
of cause, inserted in edition K of the Inquiry— 1753- 
54— "is identical with the traditional doctrine" of 
causation. And Selby-Bigge^ contends that this 
clause added "in italics can hardly be regarded as a 
paraphrase or equivalent of the main definition" in 
the Inquiry. It is usually unfortunate for critics 
to differ diametrically with their author in the inter- 
pretation of his language. In edition K of the In- 
quiry, after defining cause as a philosophical relation, 
Hume added the following sentence:* "Or, in other 
words, where, if the -first object had not been, the 
second never had existed." Of course, it might seem 

1 Hume's Enquiries, pp. xv, xvi. 

2 PMl. Rev., Vol. VII, p. 47. 

3 Hume's Enquiries, Introd. * P. 63. 



THE IDEA OF CAUSE AND EFFECT. 161 

to a casual observer as if this new definition were 
"identical with the traditional doctrine" of causa- 
tion, or at least as if it were not an "equivalent of 
the main definition in the Inquiry." But Hume re- 
garded it as being identical with his doctrine of 
causation; it is his own definition of cause expressed 
"in other words." Furthermore, it may be noted 
that Hume fairly guarded himself from a mistaken 
interpretation like that of Peterson or of Selby-Bigge 
when he remarked, in a note on the succeeding sec- 
tion:^ "If a cause be defined, that which produces 
any thing; it is easy to observe, that producing is 
synonymous to causing. In like manner, if a cause 
be defined, that Jjy which anything exists; this is 
liable to the same objection. For what is meant by 
these words, hy which? Had it been said, that a 
cause is that after which anything constantly exists; 
we should have understood the terms. For this is, 
indeed, all we know of the matter. And this con- 
stancy forms the very essence of necessity, nor have 
we any other idea of it. ' ' 

Brede^ states that, in the Inquiry, there is a higher 
estimation of the worth of the causal inference than 
in the Treatise. On the other hand, Selby-Bigge 
asserts:^ "The distinction [between natural and phi- 
losophical relations] in the Treatise is indeed most 
bewildering, but, with its disappearance in the En- 
quiry, the relation of causation becomes more com- 
pletely subjective." While Peterson* affirms that, in 
the Treatise "the subjective aspect is made still more 

1 P. 78. Der Unterschied d. Lehren H., p. 39. 

* Hume's Enquiries, p. xvii; cf. p. xv. 

* Phil. Rev., Vol. VII, p. 45. 



162 Hume's treatise and inquiry. 

prominent" than in the Inquiry. The correctness or 
incorrectness of these conflicting assertions can be 
shown only by appealing to the author himself. No 
doubt it is tedious to resort continually to quotations. 
But there is no other method of dealing with the 
question under discussion. The subject will be dealt 
with as briefly as possible. In the Treatise Hume 
asserts:^ ''We have already taken notice of certain 
relations, which make us pass from one object to 
another, even though there be no reason to determine 
us to that transition; and this we may establish for 
a general rule, that wherever the mind constantly and 
uniformly makes a transition without any reason, it 
is influenced by these relations," The relations are 
resemblance, contiguity, and cause and effect.^ But 
cause and effect arises from resemblance and constant 
conjunction, that is, from resemblance, contiguity, 
and custom. And the causal inference is produced, 
not by the relations of resemblance and contiguity 
simply, but by the repetition of these relations, that 
is, by custom. Hence Hume says later, "all reason- 
ing concerning matters of fact arises only from cus- 
tom."^ In the Inquiry he states:* "Though we 
should conclude, ... as in the foregoing section, 
that, in all reasoning from experience, there is a step 
taken by the mind, which is not supported by any 
argument or process of the understanding, there is 
no danger, that these reasonings, . . . will ever be 
affected by such a discovery. If the mind is not en- 
gaged by argument to make this step, it must be in- 
duced by some other principle of equal weight and 

1 P. 392. 2 p. 393. 

3 P. 487 ; cf. pp. 444, 475. * P. 36. 



THE IDEA OF CAUSE AND EFFECT. 163 

authority." This principle is ''custom or habit," a 
principle which determines one to draw the causal 
inference when one has lived "so long in the world 
as to have observed similar objects or events to be 
constantly conjoined together."^ 

It is now necessary to discover the nature of cus- 
tom, to learn if it is of ' * equal weight and authority ' ' 
with reason. In the Treatise, the author does not 
give any satisfactory account of this principle. In 
a general way he regards it as the repetition of a 
number of particular instances,^ but more specifically, 
as a quality of mind or mode of activity resulting 
from the repetition of the same experience.^ He 
sometimes uses reasoning synonymously with custom, 
speaking of it as "a wonderful and ^^nintelligible 
instinct" in the soul, a principle of nature that is 
common to man and beast.* He even holds custom 
to be more trustworthy than reason proper, or the 
understanding. ' ' By the same rule, ' ' says Hume,^ as 
the skeptic "continues to reason and believe, . . . 
he must assent to the principle concerning the exist- 
ence of body, . . . Nature has not left this to his 
choice, and has doubtless esteemed it an affair of too 
great importance to be trusted to our uncertain 
reasonings and speculations." Belief in "the exist- 
ence of body" arises from custom and imagination.® 
In Part IV, it is true, the author— in a criticism of 
the "faculty, which judges"— professes to reduce, by 
"the rules of logic," probable reasoning, that is, the 
causal inference, to "a total extinction of belief and 

1 P. 37. « Pp. 458, 459. 

3 P. 403. * Pp. 470, 471; cf. p. 403. 

6 P. 478. 6 Pp. 487, 488. 



164 Hume's treatise and inquiry. 

evidence."^ But he immediately adds: "Should it 
here be asked me, whether I sincerely assent to this 
argument, . . . and whether I be really one of 
those skeptics, who hold that all is uncertain, . . . 
I should reply, . . . Nature by an absolute and un- 
controllable necessity has determined us to judge as 
well as to breathe and feel; nor can we any more 
forbear viewing certain objects in a stronger and 
fuller light, upon account of their customary connec- 
tion with a present impression, than we can hinder 
ourselves from thinking as long as we are awake, or 
seeing the surrounding bodies, when we turn our eyes 
towards them in broad sunshine," Yet, in another 
place, Hume admits that custom is at times the ground 
of illusion, and "may lead us into some false com- 
parison of ideas. "^ Thus in the Treatise, belief in 
the existence of body is "an affair of too great im- 
portance" to be entrusted by nature to "our uncer- 
tain reasonings and speculations"; it is entrusted to 
custom and imagination. And the causal inference 
is determined through custom or instinct with an ab- 
solute and uncontrollable necessity; yet custom is 
sometimes false or illusive. The case is exactly sim- 
ilar in the Inquiry. For instance, Hume asserts:^ 
"I shall add, for a further confirmation of the fore- 
going theory, that, as this operation of the mind, by 
which we infer like effects from like causes, and vice 
versa, is so essential to the subsistence of all human 
creatures, it is not probable, that it could be trusted 
to the fallacious deductions of our reason, ... It 
is more conformable to the ordinary wisdom of nature 

» P. 474. . i P. 415; cf. pp. 444, 547, 548. 

3 P. 47; cf. pp. 124, 127. 



THE IDEA OF CAUSE AND EFFECT. 165 

to secure so necessary an act of the mind, by some 
instinct or mechanical tendency [that is, custom], 
which may be infallible in its operations." But in 
section xil he admits:^ "We have no argument to 
convince us, that objects, which have, in our experi- 
ence, been frequently conjoined, will likewise, in 
other instances, be conjoined in the same manner; 
and that nothing leads us to this inference but cus- 
tom or a certain instinct of our nature; which it is 
indeed difficult to resist, but which, like other in- 
stincts, may be fallacious and deceitful. While the 
skeptic insists upon these topics, he shows his force, 
or rather, indeed, his own and our weakness; and 
seems,for the time at least, to destroy all assurance 
and conviction." True, in the Inquiry, Hume does 
not subject the "faculty, which judges," to the crit- 
ical examination that he did in the Treatise. Never- 
theless, as he once wrote Strahan,^ concerning the 
essays on suicide and immortality: "I suppressed 
these Essays, not because they could give any offence, 
but because, I thought, they could neither give pleas- 
ure nor instruction," so he remarks now, regarding 
the reasoning of the skeptic : * ' These arguments might 
be displayed at greater length if any durable good or 
benefit to society could ever be expected to result 
from them."^ This observation evidently implies 
that his position on this topic also remains unchanged. 
It has often been asserted, on the one hand, that 
Hume denied the possibility of a necessary connection 
between causes and effects, and on the other, that he 
denied only the possibility of a knowledge of such 

1 Pp. 130, 131; cf. I, pp. 547, 548; IV, p. 132. 

2 Hill, Letters of D. H., p. 233. » P. 131. 



166 Hume's treatise and inquiry. 

connection. Thus Knight^ declares that Hume's 
theory of causation "positively affirms that there is 
no power within the antecedent adequate to produce 
the consequent, that the notion of such causal power 
is a fiction of the imagination." And RiehP states 
that Hume never denied the existence of active prin- 
ciples in nature, but only their knowableness and 
conceivability. While each position may contain an 
element of truth, the latter is the more correct; it is 
conformable with Hume's practice, the former is the 
more consistent with his theory. Hume's language 
frequently implies the existence of external objects 
corresponding to impressions and ideas. Occasionally, 
he admits such existences. In the Treatise, he says :^ 
"I am, indeed, ready to allow, that there may be sev- 
eral qualities both in material and immaterial objects, 
with which we are utterly unacquainted." And in 
the Inquiry,* he acknowledges "a kind of pre-estab- 
lished harmony between the course of nature and the 
succession of our ideas," although the "powers and 
forces ' ' by which the course of nature is governed are 
"wholly unknown to us." Hence, he does not mean 
to deny the existence of an external world endowed 
with various powers and forces, but only the possi- 
bility of knowing it. The rationalists and intuition- 
alists maintain, of course, that he overshoots the mark 
when he asserts, as he repeatedly does, that the idea 

1 Hume, p. 159; cf. Brougham, Lives of Men of Letters in the 
Time of George III, p. 172. Koenig, Die Entwickelung d. 
CausalproMems, 1, p. 216 and n. 

2 Der pliilosophische Kriticismus, 1, p. 129 ; cf. Burton, Life, 
I, p. 81; von Kirchmann, Untersuchung in Betreff d. m. Ver- 
standes, p. 178. 

3 P. 462; cf. p. 477; II, p. 183. * Pp. 46, 71. 



THE IDEA OF CAUSE AND EFFECT. 167 

of necessary connection among external objects is a 
fiction. For to assert that this idea is fictitious and 
false is the same as to imply that there is not any 
necessary connection among objects in the external 
world. It should be observed, however, that the idea 
which Hume affirmed to be false was the rationalistic 
idea of causality. And in this respect, it will now be 
generally conceded that he was correct. Neverthe- 
less, had he contented himself with stating that such 
necessary connection, provided it exists, is unknown, 
the position would have been quite satisfactory to the 
empiricists, as well as perfectly consistent with his 
own principles. 

Finally, there are some writers^ who insist that 
Hume 's theory of causation is the same, or practically 
the same as that of Kant. The truth of this state- 
ment depends upon the manner in which it is inter- 
preted. With Hume, as with Kant, the idea of cause 
and effect is subjective, and is not valid when applied 
to suprasensible things; to this extent both agree. 
According to Hume, however, the idea is empirically 
derived, by means of the imagination, from repetition, 
custom, or instinct, and in a similar manner is ap- 
plicable to perceptions; while according to Kant, the 
idea is a transcendental concept of the understanding, 
and is a priori valid when applied within the realm 
of phenomena. With the former, therefore, the idea 
is equivalent to the invariable succession of antecedent 
and consequent ; with the latter, it contains an element 
of necessity over and above invariable succession. 
True, according to Hume, the idea of cause and effect 

1 Gf. Riehl, Der philosophisclie Kriticismus, I, p. 139; Simon, 
Berkeley's Principles of Human Knowledge, pp. 203, 206; 
Webb, Veil of Isis, p. 94; Stirling, Mind, Vol. X, p. 71. 



168 Hume's treatise and inquiry. 

contains, after a manner, an element of necessity also. 
But the necessity spoken of in this case is that which 
arises from imagination and custom, from an instinct 
which is the great guide of human life, but which, 
like any other instinct, may be fallacious and deceit- 
ful. This subjective necessity of imagination and 
custom is fundamentally different from that a priori 
necessity of the understanding for which Kant per- 
sistently contended. 

§ 30. Conclusion.— The main points in the chapter 
may now be brought together. There are two prom- 
inent elements in Hume's treatment of the idea of 
cause and effect; one logical or epistemological, the 
other psychological. The former deals with the 
ground of the transition or causal inference; the 
latter explains the genesis of the idea of necessary 
connection. 

1. The causal inference is not a conclusion of the 
understanding, but an activity of the imagination. 
It is not a logical inference, but a psychological 
process. It is not a product of reason, but of cus- 
tom. It arises on the observation of a number of 
similar instances constantly conjoined, and differs 
from a mere idea of imagination in having greater 
force, vivacity, or liveliness, that is, belief. Al- 
though the conclusion is not a valid inference log- 
ically, yet psychologically it is a necessary one. It is 
even spoken of as being superior to the "fallacious 
deductions" of reason.^ At the same time, however, 
not only does there exist a conflict between the imag- 
ination and instinct, on the one hand, and the under- 
standing, or "the general and more established prop- 

II, p. 478; IV, p. 47. 



TEffi IDEA OF CAUSE AND EFFECT. 169 

erties of the imagination,"^ on the other, but each of 
these faculties alone subverts or contradicts itself.^ 
The causal conclusion rests upon precisely the same 
basis in both works. Although the inference, or 
transition cannot be theoretically justified; yet prac- 
tically, it is indubitable, and is sufficient for all the 
purposes of life. 

2, The idea of necessary connection between causes 
and effects arises in the mind at the same time as the 
causal inference, and in the same manner, viz., from 
experience, through imagination and custom. The 
genesis of the idea has three stages, two of which may 
be called objective, and one subjective: (1) The mind 
observes a number of similar instances constantly 
conjoined; (2) as the result of this observation, a new 
feeling, determination, or internal impression arises, 
the impression of reflection of which the idea of neces- 
sary connection is a copy; (3) the idea of necessary 
connection, which at first is wholly subjective, is 
gradually applied to external objects through a 
quality of the imagination, and in this way arises the 
idea of necessary connection between object': or events. 
Consequently, the idea of cause and effect is valid as 
a copy of a subjective feeling, and is applicable to 
objects in the sense of invariable succession of ante- 
cedent and consequent; but as an idea of necessary 
connection between objects or events, it is a mere 
fiction. The genesis of the idea explains its nature 
and validity. On all these points the position of the 
Inquiry is the same as that of the Treatise. 

In the history of speculative thought, the paradoxes 

II, p. 547. 2 1, pp. 505, 511, 547; IV, pp. 125, 127, 131. 



170 Hume's treatise and inquiry. 

of one age often become the orthodoxy of the next, 
and in turn become the absurdities of the succeeding 
age. Such has been true of the idea of cause and 
effect. Invariable succession of antecedent and con- 
sequent, the striking paradox of Hume's day, became 
in a later time the commonly accepted view of causa- 
tion, and has now in turn given place to a juster 
conception, that of the equivalence of cause and effect. 
But while thought moves in cycles, these at most are 
only corresponding, never identical. The empiricist's 
criticism of causality has been made once for all. As 
Luther burst the bonds of scholasticism, Hume rent 
for ever the veil of rationalism. The philosopher, 
however, was more successful at demolishing old 
temples, than at erecting new ones. While the 
foundation which he first laid still remains, the 
Humian structure, never stable, has already crumbled 
with its own weight. It is beyond the scope of this 
work, of course, to give a derivation of the idea of 
cause and effect. Suffice it to say, that this idea is a 
product of experience. Its origin and history are to 
be sought in the life of the race. True, it passes 
through a series of corresponding stages in the life of 
each normal individual. Its dawn is unfolded in the 
conscious activity of the child. The essential element 
at this stage is producing power. The element of 
necessary connection does not arise until much later, 
sometimes indeed does not appear at all. The early 
age at which Hume wrote the Treatise is possibly a 
partial explanation why he insisted so strongly upon 
his principle that events seemed "conjoined" but not 
"connected," that it is easy "to conceive any object 
to be non-existent this moment, and existent the 



THE IDEA OF CAUSE AND EFFECT. 171 

next," without attaching to it the idea of "a cause 
or productive principle." The idea of equality be- 
tween cause and effect may arise either before, or 
after that of necessary connection, according to the 
character of the person's environment. But the idea 
of causation, in any, and every stage of its develop- 
ment, is merely a generalization, conscious or uncon- 
scious, from the totality of experience.^ 

> Cf. Schurman, Phil. Rev., Vol. VIII, p. 457-463. 



LB My '08 



Tr 



HUME: 



THE RELATIOiS^ OF 

THE'TREATISE OF HUMAK NATUKE— BOOK I 

TO THE INQUIRY CONCERNING 

HUMAN UNDERSTANDING 

THESIS 

presented to thk 

Univrr«ity Faculty of Cornell Univkksttv 

FOR the 

Degree of Doctor of Philosophy 



WIJ.LIAM BAIRD ELKlTf"^ 



ITHACA, N. Y. 
1904 



